Question about Hutt C65

The window must be at least 30 x 30 cm in size.

It depends on how big the corners are. I have a triangular window and one corner is smaller than this machine, so I should clean the window by hand.
Even with square windows you have to work/clean a little (in corners)

Overhead works, it cleaned the underside of my patio roof well.
I can't say anything about triangular windows.