You take it out of the packet and think, "There's no way this can possibly work". I have grease on my tow ball, there's nothing other than friction on the tow ball to hold it in place... It defies all engineering principles... But then you put it on (which took me about 20 seconds, the first time I tried it) and it's so solid you could sit on it without it budging. It's because you get a huge force-multiplying effect as you push the vertical bars apart, and even more as you push down the locking bar, and the rack is very well made - feels very strong.
I bought a couple of longish (85cm) bungee cords, and that holds two adult bikes with no problem at all. I used to have roof mounted racks, which cost a fortune, and eventually got rusty. I left them on the car permanently because it was a half hour job to bolt them on. This device you just keep in the boot, and it takes two minutes to fit AND get your bikes on. A truly remarkable piece of design.