Hate them. Always end up with more scratches with a cover...bits of grit getting blown inside it and the wind moving it round. Do you really need one? Bought an oxford one a good few years back. seems strong enough but the white furry lining ends up all over the bike.
Used a Motrax heavy duty one every day for last four years and has always done what it should and does not seem to have caused any scratches (not that I would necessarily notice).