These suit large, flat, accessible panes and little else. Check the safety system first: every model should have a backup power supply and a physical safety line, because the failure mode is a device falling from height. Expect to move it between panes yourself.
Safety backup is non-negotiable
A window robot holds itself to glass with suction. If power fails it must not fall. Look for an uninterruptible power supply that keeps suction alive through a cut, plus a rated safety rope anchored properly. Treat any model without both as unsuitable for anything above ground level.
It works on some windows, not all windows
Large unbroken panes are the ideal case. Small panes, deep frames, leaded or astragal bars, and heavily textured glass either block the robot or leave most of the surface untouched. Measure your typical pane before buying, and be realistic about how much of your glazing actually qualifies.
Supervision and streaking
These are not set-and-forget devices. You will place the robot, watch it, and move it to the next pane. Results depend heavily on pad cleanliness and the solution used, and edges and corners usually need finishing by hand. Judge them as a labour reducer for awkward glass, not as a replacement for a window cleaner.
Questions people ask
Can I use one on upstairs windows from inside?
That is the main use case — reaching outside glass you cannot safely access. Always fit the safety line to a solid anchor, and never rely on the suction alone.
Will it leave streaks?
Often some, particularly at edges and corners. Clean pads and the recommended solution make the largest difference.
Does it work on small or divided panes?
Generally not well. Deep frames and glazing bars stop the robot travelling, so it may clean only the centre of each section.