I've used a Specialised cover on my Golf for two and a half years now. Where the stitching touches the car on high points it makes a light rub mark which easily polishes out. Once those high spots have been dealt with using extra material it doesn't mark at all, but you have to be fastidiously clean, so it's not suitable for those with low OCD levels. And it can be a pain getting home and having to do a full outside valet before replacing the cover. But better than getting acid etching from bird shite, which seems to affect red quite badly.
