Got this on my windscreen yesterday, took a bit of time to get it on and setup and this morning when going to work was a perfect opportunity to test it out as it was pissing down.
Ok, first up, dont put this crap anywhere near your windows. If you detail much and notice what happens when you put wax layers on your car, well the exact same thing happens to your windscreen, you get beading, lots of em and you cant see sh!t. Use your wipers ? Ok, dont that, all they do is smear and your wipers 'shudder' as they are being used. If you go faster, say 40mph, it still doesnt completely clear, Id say you would have to be going pretty fast for the car windows to clear after using this crap.
Unless I'm missing something, dont use this anywhere near your windows.