IMO Rain-X provides limited help. Nothing takes the place of using your windshield wipers. The more you use the wipers the faster the Rain-X has to be reapplied. To me it's not worth the money, time and effort to apply the stuff.

A side note... when I was working on Air Force aircraft, we applied a rain repellant on the windshield that worked well with the ram air rain removal system. Didn't have windshield wipers on the big jets. :wink: