C-man,
Just a caution, glass is a lot softer than you might think, and if you would not use a dirty clay bar on the paint, then I would also not use it on the windshield.
Glass gets streaks, chips and swirls just like paint. it might be a little more durable, but if your paint gets messed up at least you don't have to look through it.
All I am saying is don't take the durability of the glass for granted.