Rain-X works pretty well if the windshield is cleaned well and it's properly applied. How well the stuff slides off of the windshield depends upon the car and its aerodynamics. Many years ago, I had a car that I tried it on, and it didn't seem to work. I did it a second time and it worked really well. Water beaded up on the windshield and then when I hit 45mph, just blew right off, but I still used the wipers if the rain was heavy enough. Below 45, the water beaded, but didn't really blow off. My boxster has the water blow off at a different speed, but I can't remember what speed that is.
Applying regular Rain-X is a PITA. I have switched and been using for years, Rain-X that you put in your windshield washer fluid. THat way every time you squirt your windshield, it gets re-applied. You can even give it a squirt in the rain and see a difference if it doesn't seem up to the task. I still use my wipers, but it makes a huge difference in visibility through the windshield whether you're using your wipers or not.
A while back, I had the pump for my washer die in a year with a drought. It was dead for 6-9 months, and by that time, my windshield had lost all Rain-X functionality, but I didn't realize it because I never drove in the rain. I drove home from work one day and it started raining. I couldn't see carp. I had just got the windshield pump fixed, but the tank only had washer fluid, no Rain-X. WHen I got home I added some of the fluid additive. The next time I drove in the rain, the difference was huge.
If you find something that REALLY means that you don't have to use your wipers, let me know, but I'm not holding my breath.
