this id the info I have received from Erik @ Osren
"As of now, the safest and most effective method to remove watermarks on the cars' windshield/ glass is to use the Osren Glass Polishing Disc with Osren Stain-X Plus (cream-based) without leaving any marring onto the glass surface.It works best on a Dual Action Polisher. The Stain-X on the other hand is a acid-based cleaner. It works very fast, however it is not safe to work on the front windscreen of cars as it will haze the entire glass."
I wanted to order from him thru' a friend going to Malaysia (but he never went). And in the end I got a small tube of Sonax glass polish at home.
when it's over I'm sure to place an order.