These two Bissell carpet cleaners are hot selling items.
The Bissell Revolution HydroSteam Pet has water heater, can generate steam while the Proheat 2X Revolution Pet Pro does not have a water heater, cannot produce steam, it has the Heatwave which uses motor heat to help maintain the water temperature during cleaning.

• Performance
  The Bissell Revolution HydroSteam Pet does a better job removing stains on carpets.
• Build Quality
  The Bissell Revolution Hydrosteam has better build quality, thicker plastic, is heavier and more robust.
• Control
  The Bissell Revolution HydroSteam has more convenient control. Its power button and cleaning mode switch are located on the handle for fingertip control. Whereas the
  Proheat 2X Revolution Pet has them on the main body.
• Cleaning Modes
  Both have 3 cleaning modes, but they are different.

  The Bissell Revolution HydroSteam has 3 modes:
  Steam Pretreat mode to loosen tough stains, brush rolls and vacuum motor will shut off in this mode.
  SteamWash Max Clean mode – use water, formula, and steam to clean your carpet. Steam is present but not visible in this mode. Carpets will dry in about 8 hours.
  Quick Dry mode use water and formula for a quick clean. Carpets will dry in about 30 minutes.

  The Proheat 2X Revolution Pet Pro has Max, Deep and Express Clean Mode.
  MAX or DEEP Clean Mode delivers a deep clean to the carpet, Express Clean Mode provides a lighter clean that dries in about 30 minutes.

• Foot Display
  The Revolution Hydrosteam has LED foot display illuminates which mode is using.
  The Proheat 2X Revolution Pet Pro does not have the display.
• Noise Level
  When setting to SteamWash Max Clean, the noise level of the Revolution Hydrosteam is louder.

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Read manuals for more details:

Proheat 2X Revolution Pet Pro Plus manual:
https://bissellcdn.blob.core.windows.net/cdn-storage-container/Web%20Portal%20User%20Guides/US/3588F.pdf

Revolution HydroSteam Pet manual:
https://bissellcdn.blob.core.windows.net/cdn-storage-container/Web%20Portal%20User%20Guides/US/3432.pdf

More info:
The Bissell Revolution HydroSteam only has steam on the foot, but no steam through the hand tool.

Tools are interchangeable.

The Bissell Turboclean Powerbrush Pet 2805 and 2987/2910/2806 are basic carpet cleaners, they work functionally the same. However, there are some difference between them:
(The 2987,2910 and 2806 are almost the same except for color, and the 2910 PowerForce PowerBrush Pet Carpet Cleaner is exclusive to Walmart.)

Edge Bristles
The 2085 has edge bristles to help clean along baseboards and around furniture whereas the 2987/2806/2910 does not have.

Collapsible Handle
The 2085 has collapsible handle for storage to fit into small spaces whereas the 2987/2806/2910 handle does not collapse.

Clean Tank Capacity
The 2987/2806 has a clean water tank capacity of 5/8 gallon while the 2085 has a 1/2 gallon tank.

On/Off Control
The 2987/2806/2910 uses a button control whereas the 2085 uses a foot pedal control. The button is located at the place that you need to bend over to reach, so the foot pedal is more convenient to turn on/off.

Clean Water Tank Position
The 2987/2806/2910 clean water tank locates at the front side of the upper part, the 2805 clean tank locates at the back.

Cord Storage
The 2987/2806/2910 power cord wraps at the back side of the upper part, the 2805 cord wraps on the side.

Power Specs
The 2987/2806/2910 power rating is 4.75 amps versus 3.4 amps on the 2085.

Cleaning Path Width
2987/2806/2910 has cleaning path width of 7.5-inch versus 9.5-inch on the 2085.

Color
The 2987/2806 is Black & Charcoal Gray with Electric Green & Grapevine Purple Accents,
2910 is Black & Charcoal Gray with Grapevine Purple & Electric Green Accents,
the 2085 is Titanium with ChaCha Lime Accents.

Similarities:
* They have two tank system: separate clean water tank and dirty water tank.

* Roll with 4 rows of bristles to scrub messes up and off carpet and area rugs.

* No brush on/off control.

* Lightweight, less than 12 pounds.

* Have removable nozzle, but Not easy removable brush cover.

* 20-foot power cord.

* Comes with a trial size bottle of formula.

* Carry One-year limited warranty.

* There is NO hose or hand tools included. If you need something with hose and tools for cleaning above floor areas, you should look at other machines such as the
Bissell ProHeat 2X Revolution Pet Pro 1986

* Though there is a removable nozzle, it is not mean that you can access to the the roller by removing the nozzle. Because there is another layer under the nozzle which is not detachable without the help of tools. To clean the brushroll, you will need to flip the machine.
If you want to remove the brushroll, you need to use a screwdriver.

For other details, you can download the manuals to learn more:

2897/2806 user guide:
https://support.bissell.com/app/answers/list/p/174899/c/26115

2085 PDF manual:
https://support.bissell.com/app/answers/list/p/67375/c/26115

2910 guide:
https://support.bissell.com/app/answers/list/p/174900/c/26115

When trying to remove spots and stains from carpeted staircase, upholstered furniture, car interior, etc. , one of the most suitable machines to use is a carpet cleaner.
You can use a full size carpet extractor with a hose and a hand attachment to tackle those messes, or use a much smaller and lighter portable one to get the job done.

Generally speaking, a big size carpet washing machine, such as the Bissell Big Green BG10, is much more powerful and suitable for whole room carpet cleaning while the portable lightweight machine is a better option for removing small stains and spots.
Tough some big carpet extractors come with attachments, such as a stair tool and a stain scrubber, to tackle different cleaning jobs, you probably would not like to drag a bulky machine which weighs over 40 pounds to clean the few stains on the sofa, let alone carry the big guy up and down stairs to clean the steps and landing.

If you are are interested in buying a portable spot and stain removal shampooer for rugs, rv interior, upholstered surfaces, you can take a look at the Bissell SpotClean Pro 3624, it is one of the best selling and top rated portable carpet spot removers on the market.

image from Bissell infomercial

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If you do not like to use a machine, but prefer to clean by hand, you can consider carpet spot remover kits such as the Folex Instant Carpet Spot Remover Kit.

About the Bissell SpotClean Professional Portable Carpet Cleaner Machine 3624:

• This is a 13-pound portable spot and stain cleaner for carpets, area rugs, stairs, upholstery, car interiors, and more.
  
  

  image from Bissell infomercial

• It is corded, has a 5.7 amps motor and a 20-foot power cable.
• For removing pet urine, poo, puke and other stains, embedded messes, it features a 5-foot hose, comes with a 6-inch Stair Tool designed specifically for cleaning stairs, a 3-inch Tough Stain Tool for scrubbing and suctioning away the stubborn messes.
  

  image from Bissell infomercial

• And it also includes a trial-size (8-ounce) bottle of detergent to help remove ground-in stains. Its tanks can hold up to 96 ounces.

How to Use the Bissell SpotClean Pro:

1. Pretreat the soiled spots if needed.
2. Filled the clean tank with water and formula.
3. Attach a hand tool to the hose.
4. Use the hand tool to spray, scrub, and lift away the stains.
5. Empty tanks and clean tools before storing.

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Read Users Reviews at Amazon

Some Questions and Answers:

• Does this SpotClean Pro heat up the water?
  No. It does not have a heater. You fill it with hot water.
• Does it steam?
  No, it is not a steamer.
• Can you use it as a dry vacuum?
  No.
• Is it as powerful as a vacuum?
  The suction power is weaker than a vacuum.
• Does it pick up pet hair?
  It is not a vacuum, and you should vacuum to remove loose dirt from spots to be cleaned before using this machine.
• Does it have a powered rotating brush?
  The two tools included have stationary brush. And there is no motorized brush tool available for this machine. However, there is optional turbo brush that fits this machine.
• Can you use it to get rid of stains on car seats?
  Yes. Definitely.
  
  

  image from Bissell infomercial

• Can you use it to clean couch?
  Yes.
  
  

  image from Bissell infomercial

• Can you use it with water only to remove stains?
  You will not get good result without adding formula.
• Do you have to use formula from Bissell?
  Using non Bissell formula will void the warranty.
• Can you use it to clean an entire loveseat?
  It will take a lot more effort than spot cleaning.
• Can you leave the clean water in the tank after use if you do not use up the cleaning solution?
  This may cause mold, leakage, even damage the machine. And if you use the remaining solution to clean the next time, it will be at room temperature, you will not get good performance.
• Can it clean the spots by itself?
  No. You can check out the Bissell SpotBot which has a hands free cleaning mode.
• Is the hose detachable for cleaning up?
  No. Try to suction up some clean water only to clean it. Or buy the HydroRinse Self Cleaning Tool to clean the hose. The HydroRinse Self Cleaning Tool is designed specifically for cleaning the hose after each use.
• Does it suction up liquid?
  Yes.

Bissell 3624 SpotClean Pro instructions:
https://support.bissell.com/app/answers/list/p/67257/c/26115

Specifications:

Bissell SpotClean Pro 3624 Specifications

All of these machines are mini carpet shampooers for spot and stain removal in area rugs, carpets, upholstery, etc. If you are a Bissell fan and deciding between these stain extractors, the following info may help you make an informed choice.

Bissell SpotClean vs Little Green vs Spotbot vs Pet Stain Eraser what’s the difference and which is the best to buy?

Based on thousands of users reviews, the Bissell Little Green, Spotbot, and SpotClean have higher rating than the Pet Stain Eraser. However, each one has its pros and cons. Just pick the one that fits your needs and preferences.

Pet Stain Eraser
Among these different mini stain removal machines, the Pet Stain Eraser is a bit different from the others.
The other 3 have hose and hand tool to clean messes while the Pet Stain Eraser does not include these accessories, the Pet Stain Eraser machine itself is a handheld tool. It is much lighter than the other series machines. And the tank is much smaller, holds only 8-ounce of liquid.
The biggest difference between this one and the other three series is the power source. The Pet Stain Eraser is battery powered while the others have no cordless models available at this moment. Depending on which model you buy, charging will take about 4, 4.5, or 8 hours, running time will be approximately 15, 20, or 30 minutes. The old models use stationary brush while the new Pet Stain Eraser PowerBrush version can use powered rotating brush or stationary brush.
The biggest Pro of this handheld carpet extractor definitely is the cordless feature, especially for those who prefer a no cord portable machine. However, many users report that this one is easy to have leaking issues and has weak suction to pull up all the liquid. Some leakage problem may be caused by using it at a incorrect position. To prevent leaking, you should ensure the machine is always in a horizontal or in an upright position. This makes it not as easy to control as using a hose with a scrubbing hand tool, since you have to keep it at the right angles, the weight is much heavier than using the hose with hand tool.
The old version is proved that it is not a good choice by users experience, if you still want a cordless, you could have a look at the new version Pet Stain Eraser PowerBrush which was released in 2020 to see if it works better.
However, unless you prefer a battery powered one, you will want to consider the other three.
Read the Bissell Pet Stain Eraser models comparison for more information.

SpotBot
This is the only series that have 2 cleaning modes: Manual cleaning and Hands Free cleaning.
Its automatic cleaning cycle has two options: Quick Clean or Deep Clean. When sellecting the automatic cleaning mode, you get the jobs done hands free. You do not have to use the hand tool to scrub the stains, instead, you press a button to select which cleaning cycle, Quick Clean
or Deep Clean, you would like to use. The machine will automatically spray, brush and suction the soiled area.
When selecting the manual mode, you use the hose with a stain removal hand tool to spray, scrub, and suck up the solution manually.
If you are tired of scrubbing on your hands and knees, then you will be interested in this Bissell SpotBot. With the hands free mode, you just place it over the stain, set it and walk away, and then let it clean the stain for you. However, when using the hands free mode, it can not be used to clean upholstery or auto seats or similar surfaces. You have to use it on a level surface.
Read the Bissell SpotBot models comparison for more information.

Little Green and SpotClean
The Little Green series and SpotClean series have some similar models. For the similar models, you can pick the one with color you like, or one with lower price from the two series.
Both of these two series have different models such as the ProHeat model and Pro model.
Based on users reviews, the SpotClean Pro is one that deserves a close look. It is more powerful than most other models, has a 5.7 amps motor while most others have a 3 amps motor. And it has a 0.75-gallon tank, much larger than some other models which only have a 37-ounce or 48-ounce tank.
If you want to remove liquid spills, blood, pet urine, and other stains and spot from car seats, sofa, carpeted staircase, and similar soft surfaces without washing the whole things, the Bissell SpotClean Pro 3624 portable carpet cleaner machine plus proper shampoo is a good option.
For those who looking for a smaller one that works well, you can have a look at the original Little Green.
Read the Bissell SpotClean models comparison, Little Green models comparison for more information.

Overall, a portable carpet cleaner machine is a better choice than a full size machine when cleaning stains and spots, it is cheaper, lighter, more convenient, and takes less effort to tackle small jobs effectively.
If you are deciding between the above Bissell small carpet & rug shampooers, you can:

• consider the Pet Stain Eraser PowerBrush if you like a cordless cleaner;
• check out the SpotBot if you hate scrubbing on your hands and knees;
• take a look at the SpotClean Pro if you want a small but relatively powerful carpet shampooer that works;
• choose the original Little Green if you want one of the best selling and rated little rug stain remover machines.

More info on these small spot cleaner machines:

• All of the above available models have no heater to heat up water, including those ProHeat models. To get satisfied cleaning performance, it is recommended to use hot water rather than water at room temperature.
• They are not steamer so they do not steam or sanitize the surfaces.
• The manual states using any Non-BISSELL cleaning solutions, any cleaning formulas which contain lemon, pine oil or vinegar harm the cleaner and void the warranty.

For whole room wall to wall carpet cleaning, you need a full size carpetcarpet. If you have no idea which one to buy, have a look at the Bissell Big Green BG10.