I used to use Rain-X on all my cars. The biggest advantage I saw with it was that ice and bugs were easier to remove, especially so after a fresh application. Sure it helped the water bead up but I still used the wipers.
At some point I started becoming aware of glare during rain events, especially sun showers. I decided that it was due to the beading effect of the Rain-X treatment. When a wiper sweeps the window it leaves behind a thin film of water, normally this is optically clear since it just wets out on the surface. With the Rain-X it seemed to form millions of tiny beads somewhat like when you have interior fogging of a window. I remembered that the cure for fogging SCUBA masks is to polish them with soap so as to make the beading water wet the surface and become optically non-distorting (the opposite of Rain-X). Once the Rain-X faded I never saw this issue again. I saw this effect on several cars and my motorcycle helmet visor too.
Ultimately I have come to the conclusion that I don't want ANYTHING on the glass to guck up the wipers. Some of the automatic car washes spray stuff on the car during the final rinse too so I try to avoid them too. I do miss having the ice slide off the windows though here in MN!