Well, with a conventional lensboard and the front mount I can't bring it to focus further than about 18" in front of the lens on my 8x10, and on the 5x7 it won't quite reach infinity. I'll need to get my wife to fire up the wood shop for a recessed board, but I can sanity-check its performance at portrait distances on the 5x7 this evening.
The good news is that at the point-blank range where I *can* focus the 8x10, I don't think I've hit the mechanical vignetting from the shutter. It may actually work as it is for macro use, although I don't know that its performance in that role will be too exciting. Dan, have you tried it for macro work in, say, the 1:1-2:1 range?