I've had a Thule 945 towball mounted rack for a few months now.
Getting the rack on and off the car is very easy, and it folds down to fit in the boot OK.
It has a tilt function so getting the hatchback open is no real problem.
If you have a 56cm road bike you will probably have to clamp onto the seat tube rather than the top tube, and you may need to do some experimentation to find a combination that works. This could be a real problem with the 3 bike model. Best to try before you buy.
The drag and wind noise is much better than a roof rack.
I haven't had a long trip in rain yet, so I'm not sure how the bikes will look afterwards. I hope it avoids the car wash effect of the roof rack that removes all lubrication from the drive train, but I suspect that the biked will end up filthy from the back spray.
Last long trip I did, my wife's bike ended up with a loose handlebar clamp. This *may* have been caused by vibration due to the rack being cantilevered from the towball. We will be doing about 3000km in a couple of months time, so I'll see if anything rattles loose on that trip.
Main reason I got the rack was to reduce the drag at highway speed, and to make it easier to fit the rack and to put the bikes on and off. The first two aims have been satisfied, but I find it's still a bit fiddly getting the bikes secured properly.
Overall I'd give it 7/10