I have the Flash Unit Coupler for Demi on my Canon 7. Paid $20.00 for it at Pacific Rim Camera. There are two issues with it. First of all, it is just a hair too small for the Canon 7. I had to spread the legs of the clip to get them to fit over the flash connector socket and it completely blocks the socket, so you cannot use a flash with it. Secondly it places an auxillary viewfinder directly over the film rewind knob about 1/'2 inch above it and blocks it. You have to remove the clip to rewind the film. I find it more of a hassle than a convenience. If the widest lens you use is 28mm, I recommend that you simply use the 35mm lines and know that the shot will actually encompass a little more than you see. If you are using anything wider then the Demi clip is better than nothing.
John