I use rainX, and also sometimes (when I misplace the bottle) a competing product called Rain Slick by 20/10, which is cheaper. I can't tell any difference between the two.
Watching the raindrops bead, run, and blow off is interesting. I still find I can see a bit better if I run the wipers and wipe the drops off entirely. I guess I could 'get by' without wipers but since I have them, why not use them? Safer, you know. For you and me.
The RainX does make my wipers work better - synergistic. This makes me think about the windows on the sides or rear that don't have wipers: is there any product that would make rain 'sheet' for these windows? A clear sheet might be easier to look through than a speckly beaded mess?
This is an effect i also remember from my motorcycle days, where I'd draw my glove constantly across the faceplate - not so much to wipe off all the rain but to smear the drops so I could see, because they act like little lenses.
Little lenses! Obscuring my VIEW!!