I've had an RDX 450 for my T1i/500D for a year and it's worked out really well. The only weak point is the tray that screws into your tripod mount and holds the camera in the housing-- if you're not careful it won't click in all the way, and then the shutter release might not depress all the way. I haven't had any problems with the optical cable popping out.
I also have the Grip Stay L. It costs too much and weighs too much, but otherwise it's very well designed, and I wouldn't take my housing without two handles. I don't mind taking it off to open the housing. It's easy to remove (when you want to). I'm considering copying the design and machining a replacement in delrin with buoyancy handles. For now I use zip ties to attach some Stix floats.