I've got one of these:
Amazon product
It's only a "three seater" though. It's quite a bit cheaper than the Thule equivalent. However, you pay for it in lack of convenience. Just webbing straps to secure the bike wheels, no fancy quick-release ratchet clamps. Also, a hoofing great bolt to tighten it on to the towball each time you use it. Other than that, it's OK though. Can be a bit of a squeeze getting three bikes on AND making sure they don't chafe against each other. Ironically, I'd just nipped out to my local Halfrauds this morning to get a new rear numberplate to put on it for the Freelander....
...won't bother fitting it now...
Irritatingly, I'd promised to take the wee lad and his mate mountain biking tomorrow. Will still do it, but just hope the towbar on my old Alfa is strong enough! (Well, the towbar will be strong enough, it's what it's attached to that I'm worried about)!