The VW ones look nice but most mountain bikers seem to use Fiamma
I don't think there's any particular reason - just that theyre cheaper!
You can secure the bike if you double loop thru the frame and wheels though I don't know what an insurance firm will think if the bike is stolen from the rack. I personally secure them to the wheel when I'm staying over night
Just been looking at these options myself. If you want to look at the huge range that is available this site has most of the common makes, though does seem to be missing Fiamma for some reason! http://www.skidrive.co.uk/cycle/index.php good range of tow bar and rear mount systems to suit most pockets.