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 and more accurate 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.
