Rain‑X® Original Glass Treatment claims to “dramatically improve wet weather driving visibility. Simply apply the treatment to exterior glass and watch the raindrops fly off your windshield while driving. Rain‑X helps improve visibility by repelling rain, sleet and snow.”
I use Rain-x on my own vehicle windshields. It does work as claimed. With regards to windshield repair, Rain-X presents a problem. The synthetics used in the composition create a sort of waxy film on the surface of the windshield. When a rock hits the windshield, the surface glass is propelled inward by the force. Rain-X treated glass finds its way into the rock chip which makes it very difficult for the acrylic resin used in the repair process to uniformly fill the damaged area. I’m not suggesting that this is a reason not to use Rain-X. Rather, it is important to tell the windshield repair technician ahead of time that the windshield has been treated with Rain-X so the technician can take measures to dissolve the Rain-X before attempting to complete the repair. Dissolving Rain-X is as simple as using a dry-tool, which most windshield repair technicians already use for drying moisture before filling a rock chip. Filling a repair without dissolving Rain-X first will result in a cloudy appearance and a rock chip that has not been uniformly filled.
I recommend using Rain-X products. They are terrific and they work. Make sure to tell your windshield repair technician that you have used these products before the technician begins the repair.