I can't comment on J carriers because I don't use them, but perhaps I should. The design weakness with Thule is the square bars, which only becomes a problem on curved roofs, but as the roof curves so must cradles cant away from each other, reducing contact between boat hull and cradle to inside edges. The cradle faces are absurdly small to start with; this rotational deviation from level makes it even smaller. Couple that with Thule's comically inadequate détente angle fixing clamp (for holding the saddle in the shape of your boat hull) and for support you are probably better off using foam blocks. So J carriers may work better on a curved roof, if I can lift that high. I've seen some people use them for composite boats so it might be OK.
Also, poke holes in dead tennis balls and jam them on the ends of your bars. It will keep your passengers from clonking themselves, not just because they are softer and rounder than factory caps, they are bright. It's easy to lose track of exactly where black-on-black bar ends are in space, even when you're looking for them; it's hard to overlook glowing lime-green spheres. You'll have to replace them each year as they fade; remove the factory caps beforehand so you won't pull them off inside the tennis balls.
I contacted Thule's tech services and was told that the aluminum mounting clamps would not hit the field until March 2003 and that it might be late March at that. They will still have the capability to clamp to bars up to 2.5" wide. They will still ship with 50mm and 60mm screws. They also stated that some (maybe all?) of the saddle type carriers would get a four position locking set-up that would allow them to lock nearly vertical for a shell on down to flat for a windsurfer.
Although this item might be the only choice for putting a roof rack on some cars, I don't believe that it is much of an option. I'll admit that the dealer warned me that he didn't have a very high opinion of it. He also told me he wouldn't help with the installation and that furthermore, if I wasn't happy with it, everything else BUT the Thule 477 SRA was returnable. Being a hardheaded sort of fellow, I had to find out for myself. I'd like to blame the dealer because he probably should'a refused to sell the darn thing to me but truth is, that would'a made me even more madder!
With a Thule roof rack, you’re all set to head off on your adventures and make sure you have everything you want with you. When combined with other Thule products, our roof racks are also a starting point for carrying the extra special gear that lets you live your passions – with holders for your bikes, your skis, your canoes or kayaks, and your surfboards. Not to mention extra-secure roof boxes and spacious carrier baskets for special cargos