Yep, Rainbrella must be a new product. Rain X been around for many many years and does work.
Being that tow trucks run harder in bad weather than they do in good weather due to people crashing and such, we always treat our windshields so we're ready to rock and roll with best visibility possible during bad weather.
One of our company owners will shoot your knee caps off if you use Rain X on one of his trucks. He does bring up a good point. The Rain X tends to be oily and does build up after several applications on your windshield and can make a nasty smeared mess in the right conditions. So what he does, he just uses regular paint and body car wax, and waxes his glass just like it were paint. I wouldn't have believed it if I didn't see it for myself, but it does work well and does seem to last longer than Rain X without the greasy residue after several applications.
Turtle Wax or KIT cream wax with the sponge applicator seems to work best, then buff it off with a T shirt or Micro Fiber cloth.
The wax even seems to make it harder for ice to stick to your windshield so it's easier to scrape the ice off in a winter storm. Nothing like getting a hot hurry up call and you have to scrape ice before you can take off, so we like to keep our windshields clean and ready to roll 24/7 during bad weather season.