The difference is that newer “combo” robot vacuum and mop models are designed to actually scrub your floors. Combo bots can mop and vacuum simultaneously, but for especially dirty floors, it’s best to have the option to vacuum first and then mop. I also look for the option to mop only, in addition to mop and vacuum, or vacuum then mop, and, of course, vacuum only. This is the best roller mopping bot I’ve testedThe self-cleaning brush system kept the bot from smearing any spills it encountered. It also now comes in gray (white robot vacuums are not a good idea, unless you like cleaning your robot vacuum).