I've used it, it was OK
I've since used polish that you use on the fairing paintwork, I think it contains something that protects and makes the surface slippery
(GS 27 titanium???) Do you have that in the UK?
It seems that less insects stick and it is certain that a wipe over afterwards rapidly clears the screen.
iso alcohol and plastic don't fair well together, any moreso than ammonia and plastic. I guess you could do it, and maybe the first few times there would be no noticable effects. I had a shield back in years of yonder, that over a period of time I used windex on, it clouded the shield over time. The first few times I cleaned it, I saw no negative effects, but alas, it was there!
Out of curiosity someone might want to e-mail some after market shield manufacturors and pose that ? about using Rain-X on their product and see what their response is and post it here, I may very well be proved wrong--yet again!!
I may be up your way St Louis next weekend, if a deal on a 05 fjr a friend of mine is trying to put together works out, do you know if the red birds will be playing at home next Saturday, and if so what time? (sorry bout the hijack)