Not that one, but used similar. Yes they will eventually scratch the car where the straps fit onto the boot edges etc, unless you are really careful. The wheels will probably obscure the lights on most cars as well, and if you have a third rear brake light (as most cars do these days) it is illegal to block that with bikes as well.
Having said that, of the rear mount racks I have used they were strong enough for me to hang off, but do sway a bit in motion. My personal preference is for a towbar rack, or roof racks – these strap on rear ones are my least favourite (and I have all three types in the garage at the moment!)
Other thing to bear in mind is security – a couple of snips and the whole thing comes off the car…
