Corrosion is another reason why some rain repellants cannot be used. Think about all these screws around a window.
Some products are aggressive over time, I had the habit of putting some product in my car window sprayer, and after 5 years there are 2 nice weared strips on the hood where the sprayers are. Like someone rubbed sanding paper over the paint.
Never use products that are not approved folks, that aircraft is not a car, and never rub a dry cloth over a pax aircraft windshield. Always make sure the whole window is wetted first.