1.Dont use rain repellent on your car / vehicle windscreen, because water repellent will damage your car / vehicle surface. when your vehicle / car windscreen damage you will heard annoying sound of wiper each time you use your car / vehicle windscreen wiper.
Water repellent have side effect to our car / vehicle windscreen. Water repellent will corrode your vehicle / car windscreen surface.
2. Car / Vehicle wiper have to clean it often to make sure the rubber of a wiper do not stick on some sand that cause windscreen wiper corrosion. Wiper contained sand will became like sand paper.
Windscreen have scratched is advice no to polish it, because it will corrode windscreen surface.
A good wiper is only look nice but need to clean the surface clean and quite.