I tried Rain-X on my 19 year old 240D and the rain did bead up, but my 240D couldn’t go fast enough to get the beads to run off the windshield.

Seriously, it worked fine for a few weeks but where I live there aren’t enough dry spells in the winter to re-do the Rain-X every few weeks. I don’t have a garage for the car, otherwise I could do it in there. I didn’t like the Rain-X effect on the wiper’s ability to sweep the moisture off. Seemed to leave a film.