I have never used one, as I grind all my pads on the gun. Using a jig, I am pretty certain you still need to do the final trimming by hand anyway; the big advantage is that there's no chance of hitting the finish with the disc. With a good strong light and a good wobble-free disc sander, you can reduce the possibility of messing up the stock finish. I think you'll get cleaner toe and heel angles on the pad if you grind it installed on the stock. Just may way of doing it, not nesessarily the right way; works for me.
