Sorry to burst the bubble but it can scratch windows if grit is within the brush head.
Be realistic people,its not rocket science.
hey slash,
i tried to do this myself. i put by brush head in grit, in mud, in gravel, and cleaned my glass with the various stuff in the bristles. i then turned the water flow off and did the same again. i was replacing the windows so i thought i needed to see what damage i could do. i literally found it impossible to make any scratches on my own glass, even using excessive force to the point where i was holding the brush head and scraping it up and down the window!!
of course ANYTHING is possible. weird unexpected things happen every day in the world. but we have to look at things in the balance of probabilities.
if the scratch marks match how my staff clean windows (i.e. horizontal or verticle patterns) we will replace the glass.
but if it doesn't not look like we have done it, and we know how unlikely it is that we have done it with the tools we use, then we won't.
interestingly i just had bi fold doors fitted at home yesterday and there are scratch marks in them, and they're brand new and not cheap ones. the fitter said the standard for replacement glass was if you can see the scratch from 6 feet away. if you could not the manufacturer say it is acceptable standard and won't replace them. that is brand new glass. so perfect scratch free glass is not what you are buying from suppliers.