I got them from eBay, tried to post the link but it looks like the trader is no longer active. They don't impede the window at all and there is no drilling or screwing involved. They fit by a combination of ready applied adhesive tape and metal clips, but I didn't bother using the clips as they felt like they were firmly in place. They've never caused any problems since I got them in June 17@andys.....are they easily fitted? Do they impede the movement of the window at all and is there any drilling and screwing involved.....I believe some are screwed in to the black trim down by the mirror? Where did you get them from?
Cheers!