Shark PRO Steam & Spray and Steam & Spray PRO, do the names confuse you? Are they the same thing?

Both of them have a detachable cable; feature swivel steering; can Spray Only, Steam Only, or Spray and Steam at the same time; can go cordless to Spray Only. However, they are not identical.

images from manufacturer

The PRO Steam & Spray SK460 has only 1 head,
it uses Intelligent Electronic Steam Control that offers 3 steam level options. You can press the control button to select one that suits your cleaning needs best.
its water tank holds 450ml is located at the back of the main body, you fill it with the filling flask.

The Steam & Spray PRO SS460WM and SS460D (same unit except for the color and included accessories) come with 2 interchangeable heads, one Steam & Spray Head and one Spray-Only Mop Head.
they use Automatic Electronic Steam Control which claimed to provide the perfect amount of steam leaving floors sanitized with little residue, they do not have steam modes to select manually.
the water tank holds 355ml is located at the Steam & Spray Head, this allows you to detach the steam head to fill the tank at the sink or fill it with the filling flask.

The SK460 has a longer power cord than the SS460.

Read manuals to learn more.
Shark SK460 Manual – http://www.sharkclean.com/include/pdf/manual-SK460.pdf
Shark SS460 Manual – http://www.sharkclean.com/include/pdf/manual-SS460.pdf

images from manufacturer

These Shark Steamers provide 3 cleaning modes – Steam Only, Spray Only, or Steam and Spray.
The Pro Shark Steam & Spray SK460 steam control is different from the original version SK410.
The SK460 features Shark Intelligent Electronic Steam Control which has 3 distinct steam settings, each of them is designed for different cleaning needs. With the Intelligent Electronic Steam Control, you can push a button to select between the 3 levels of steaming – SaniFiber disposable pad, MOP, and SCRUB.
Whereas the SK410 uses manual steam control, user has to pump the handle manually to get steam, this lets the user control the amount of steam needed, they call it Steam on Demand. This is the key difference between these 2 Shark steamers.

The other difference between Shark Steam & Spray SK410 and Shark PRO Steam & Spray SK460 is the Water Tank Capacity.
The Pro version has a larger water tank.
The original SK410 holds 350ml whereas the Pro SK460 holds 450ml.

Otherwise, they are the same.
Both of them have a removable power cord and integrated cleanser spray.

P.S.
The SK410L and SK410W are almost the same as the SK410, the difference is the color and accessories they come with.
The included tools and accessories may vary depends on where you buy them.

You can read manuals to learn more.
Shark SK410 Manual – http://www.sharkclean.com/include/pdf/manual-SK410.pdf
Shark SK460 Manual – http://www.sharkclean.com/include/pdf/manual-SK460.pdf

The difference between Shark Light and Easy Steam Mop S3251 and S3601 Professional Steam Pocket Mop are as follows.

images from manufacturer

1, Steam Setting
The S3601 has 3 steam settings – Dust, Mop, and Scrub, they are designed from light cleaning delicate hard floors to scrubbing tough, stuck-on messes on hard surfaces.
Whereas the S3251 has no steam settings. To get steam out, you have to pump the handle.

2, Steamer Head and Pads
The head on S3601 can be flipped over, and it uses double-sided reusable micro-fiber pads. These can double the cleaning area of the steamer without changing pads. Whereas the S3251 head does not flip over for 2 sided cleaning.
The S3601 mop head is easily detached from the mop body by pressing a release button. This allows you to quickly switching between mop heads such as the rectangular mop head and triangular mop head.
While the S3251 seems to have to use a screw driver to detach the head.

3, Tank Capacity
The S3601 has 2X tank capacity.
The S3251 holds up to 250 ml (8 oz.) versus 500ml (16.9 oz.) on the S3601.

4, Handle
The S3251 has a telescopic handle that can be adjusted to fit user height whereas the S3601 handle is not telescopic.

P.S.
Download user guides
Shark S3501 Manual – http://www.sharkclean.com/include/pdf/manual-S3601.pdf
Shark S3101 Manual – http://www.sharkclean.com/include/pdf/manual-S3251.pdf

images from manufacturer

Shark S3101 and S3501 are similar simple steamers. They work in the same way. While using them, you pump the handle to produce steam. However, there are differences between them.
1, Mop Head and Pads
The S3101 is smaller to get into smaller areas.
Their heads and pads are completely different.
The S3501 has a swivel head, the pads for S3501 fit over the rectangular mop head and provide double-sided cleaning. So after one side of the pad gets dirty, you can just flip over the head to use the clean side of the pad without switching pads. Whereas the S3101 does not have swivel steering, the pad only provides one side cleaning.
The S3501 mop head and mop body are separate parts. You can easily exchange mop heads by pressing the release button to detach the mop head from the mop body, and snap other heads.
Whereas the S3101 seems to have the head built into the mop body. So it does not allow you to use an alternative head such as an triangle mop head.

2, Water Capacity
The S3501 has a much larger tank that holds up to 450 ml (15 oz.) versus 220 ml (7.4 oz.) on the S3101.

3, Power
The S3101 is 1,550 watts versus 1,200 watts on the S3501.

4, Handle
The S3501 has a telescopic handle that the S3101 does not feature.

5, Water Filling
The S3101 has the water filling hole at the back (near the top of mop base) whereas the S3501 has it at the front (middle).

P.S.
Download user guides
Shark S3501 Manual – http://www.sharkclean.com/include/pdf/manual-S3501.pdf
Shark S3101 Manual – http://www.sharkclean.com/include/pdf/manual-S3101.pdf