Just got the Rocky Mounts Tandem rack for our new car.
I got it because it bolts into the factory cross bars on most cars with the European tandem mount kit.
I don't think the swivel mechanism is as well designed as on Yakima's tandem roof rack, but Yakima specifically says not to use their rack with factory rails, so that ruled it out for me.
Also because it's mounted toward the center of the car I can't use the swivel anyway, but with the car low, and the bike light, it's not a problem to lift it on to the rack.
It holds the bike firmly, and ultimately that's my number one priority. It also shortens to hold a single bike.
So far, I would reccomend it to anyone looking for a rack to go with Audi, Porsche, Volvo, VW, factory racks.
And to answer the comments about desecrating the car, the factory cross bars come off in about 5 minutes, and we're only going to use it for trips to the mountains, where we want to enjoy the drive getting there, and the riding also.