I've got the Hipshot - I haven't installed it yet but research suggests a couple of the little felt pads are needed.
The Babicz comes with a shim. I don't think it's curved to fit the JC arch but @AndyTravis seems to have fitted his successfully.
They work, but only just. Once they're set up you're ok, but there's just too many little issues as others have already mentioned.
My main issue is how they're suspended on stilts away from the body like an oil rig. This is mainly an aesthetic concern as they just seem so fragile.
The lack of space between the saddle and end of the bridge is a pain. Even if you use unsilked strings the lumpy wound part can still rest on the saddle.
Bottom line - Jack Casady plays these things non-stop and he gets on ok with the bridge!