I know there aren't many people on here who use roof carriers, but thought this might be interesting for some The mechanism on my existing ones was getting a bit dodgy and I wanted a solution that doesn't clamp the frame so that we can take the road bikes on there as well and won't damage the paint on the MTB where the clamp goes. I noticed these and decided to give them a try:
I have to say I'm really impressed so far, really well designed, solid and there's almost no wind howl when moving with or without the bike on. Can also take bikes with any suspension geometry and different tyre sizes including 29". Down side is they are heavy, expensive, and officially you can't take bikes with roadie-style mudguards (although I'm not convinced that there isn't a bodge)
Looks as though it could rock side to side putting stress on the wheels; strap thru the bottom bracket angle could prevent that. Won't there be movement thru the steerer? Regarding clamps scatching paint work I use a non-slip padding; worked so far for many many miles
Never had a problem using thule 591's personally, got a couple second hand and i've been really impressed. I've used them for HT, FS, roadie and 29er bikes without any issues. The best thing i've found with these has been you can buy all the bits individually if you need to replace them, rather than needing a new unit! Although these do clamp to the frame so may not suit everyone. Also you need to be careful going under low bridges.