I've got one for my RC10. It works well, but as I use a full frame Canon (the 6D), I think I get very slight vignetting with it.
From memory, to get focus, I have to place it very close to the camera, just after the OAG.
This post has made me realise that I probably should have taken more notes about my setups - I was using it so regularly before summer hit that I just remembered everything. When I eventually get out again I'll have to relearn everything.
Edit: ordered from overseas. I don't know of anywhere in Oz to get it.