Bissell 3624 vs 5207
images from manufacturer

All of these 3 Bissell portable spot cleaners have separate clean and dirty water tank, but they do not have water heater. You should fill the clean water tank with hot tap water mixed with detergent, then use the included hand tools with the flexible hose to clean spot and stains.

The Bissell SpotClean 5207a and SpotClean Proheat 5207f are the same machine, they only have slightly different tools.
The difference between SpotClean Pro 3624 and SpotClean 5207a / SpotClean Proheat 5207f are as follows.

Tank Capacity
The Pro version has larger tank capacity.

Heatwave Technology
The SpotClean and SpotClean Proheat feature the Bissell Heatwave Technology that directs the motor heat to maintain the water temperature during cleaning.
Whereas the Professional does not have this feature.

Motor Amps
The SpotClean and SpotClean Proheat have a 3 amp motor whereas the Professional uses 5.7 amps motor.

Cord Length
The Prefessional has longer power cord.

Tool
All of them come with 2 hand tools, however, the larger tool on the Professional model is a bit wider.

Weight
The SpotClean / SpotClean Proheat are lighter.

Pirce
The Professional is more expensive.

All of the carry 2 year warranty limited warranty and come with trial size cleaning formula.