I went a different route with my machines. Since I like to do the Flipper Fidelity animated led panels on all my games, I fabricated a bracket and wired in a push on/push off switch that you activate by pressing the right side coin return button. The bracket is held on by the same factory thumbscrews that hold the coin mechs and the the switch is wired into the plug and play harness that comes with the Flipper Fidelity kit so it is a completely reversible mod.
Now I just turn off the back-glass lighting all together when I play. Its easy for anyone to do (or undo) and you don't have to open the coin door or make any other modifications to the machine. Makes a HUGE difference having zero glare. I didn't realize how much of the playfield I was used to not being able to see on each game.
I had piece of PDI glass and was not thrilled with the results since it only reduces the glare... sold it the very next day. In all fairness, the new owner seemed to be "okay" with it.