I've got two whitewater kayaks up on it. Holds the things solid as a rock. I just did 500miles with them up there and didn't worry about them the entire way.
Jeep Grand Cherokee with a standard roof rack.
My only gripe is that you need to be nimble to attach things to it, in that I have to pretty much get up on the roof.
I used a couple of swim noodles as cushions and they work great.
I've used J-racks before, and I would say this is as comprable to them and I think in the kayaks sit as snug.
This is an awesome value rack.