All I know is glass is very brittle as compared to urethane and it doesn't conduct and spread the heat anywhere as good as metal. So the heat built-up would be more severe on glass than on the car body. I guess, for now, what the guy said is quite sound.
Anyway, I'll just take it as it is for now, with a pinch of salt, of course.
My 2cents is that heat does build up so just make sure its properly lubricated with water and as usual lah, don't keep the RB in the same place for too long (common sense la and must have spary water handy for lube) . Don't need pressure, just the weight of the RB + alittle is enough. If you can RB your car no problem you can do the glass also lah.
Just must have the right product and tools. The felt pad and diamondite is a good and easy combo. For anyone who has the skill to RB their car they can do their glass with this combo no problems. Kacang putih.
But it does take some time as glass is really hard so the product needs some time to work, minimum 1hr for the whole windscreen if the whole windscreen is swirled.