What is the smallest size window these can clean? Also, what are the main differences between the models, the descrptions don’t really give enough information to distinguish them.
Great question! All of the WINBOT 7 & ** WINBOT 8 Series Models **, (710,730,730DR & 830) can work on a window as small as 19" wide. The WINBOT 930, while larger can work on windows as small as 14" wide, because of how the Smart Move Technology works.
So, size does matter 
The other major difference, is the type of suction, and how that correlates to the type of glass to be cleaned. The WINBOT 7 series models & the W930 use vacuum suction and require a flat pane of glass. The W830 uses vacuum suction and can clean frosted glass, or glass with decals or film applied to it.
Additionally, the W710 only works on framed glass, like windows or mirrors where there is a frame present. All the other models work on framed or frameless glass.
Hope that helps with your choice.
Here’s a video of the W930 in action
[youtube=Q2xeQDjNPLY][/youtube]