Installed a Pinwoofer Super Kit last night on TMNT. It's definitely a substantial sound upgrade! Bass and back box speaker clarity are significantly improved. Besides the actual end result I was most impressed by just how well the entire kit is put together and layed out. This is probably the most professional put together mod I've seen since joining this hobby.
On another note I put a piece of Invisiglass from Dialed In on TMNT premium. I noticed a lot of glare from the back box / translite to the point it made seeing the center upper playfield area difficult to see. Invisiglass helped cut down the glare a good amount. The standard glass went into Dialed In for now lol.