Hi....I have one of those racks, bought it 20 years ago when I first started cycling,
....barely used it, bought something better second hand, then bought a rack that fixed to tow ball.....much preferable.
It's ok for a light bike, wouldn't want to put 3 on.
...check out ebay for something better.
If you decide to buy it, get a couple of extra straps with the hook on from Halfords....make it more secure.
Don't worry about it scratching paintwork, I think the hooks are plastic covered anyway , just put a few strips of insulation tape where the hooks fit.
....Mike