There's a lot of room for expensive mistakes when grinding the pads. I don't get as good of results on the jig as on the stock.... but that means we're only one thickness of tape from disaster.
Your experiences echo mine... But that last 'thickness of tape' I did by hand - part on the stock and part off the stock...
I sold the jig. It just wasn't worth having. Last pads I installed were $75 + the pad..