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. It also now comes in gray (white robot vacuums are not a good idea, unless you like cleaning your robot vacuum). I write The Verge’s Best robot vacuum buying guide and the Best budget robot vacuum guide, and for this guide, I tested 15 different mopping robots.