I've been using RainX for three years now with no problem that I have noticed on our R25. It works excellent, as I am sure others on this forum will tell you. If I am travelling a lot on a given day or I know it is going to be a little rough I make sure I do a fresh application. The glass is tempered and tinted and, if a glaze is applied, it is done at a very high temperature to I don't think RainX will have any effect, as experience shows.
The glazing seems to refer to the amount of tinting in the window
http://www.diamondseaglaze.com/upload/t ... ptions.pdf . The hardness of the glass is the result of tempering. The quality of their glass is excellent. Much better then a car's glass, where RainX is usually used.