This can be important when you want to avoid the splattering of dirt particulates all over the place. Some items require a more dispersed steam - large areas, plant misting, upholstery. The lower priced units either do not have this feature or have a dial control on the canister. Length of warranty on boiler and other parts. It is usually 3 years on a good residential vapor steam cleaner and 5 years on a commercial vapor steam cleaner.
Some units have a lower price because they only come with a one year warranty.
Be sure to check this out. These vapor steam cleaners need a good handle for easy lifting up stairs. Somebody needs to have really paid attention to this design feature. If you live in a multi-floor home or will be cleaning on different floors check out how easy it is to carry the vapor steam cleaner. Are they decent sized for easy maneuverability.