Hah! I can never get it to go down well enough, it always looks ugly, and if you mess up once you're probably not getting it off again.

Playfield protectors are much safer and easier, but they can have as slight affect on the game. I've never noticed it playing different though, but it's a personal preference thing

Playfield protectors are sheets of thin clear plastic/lexan/etc. They don't attach at all, they just sit on top. If installing a protector, you don't want to wax, as it'll cloud. If applying mylar, you want to wax first, as it'll make removing the mylar a bit easier and mylar doesn't cloud like that.

It's not that hard to make your own protector. Buy a blank sheet for about $20, lay it on top and trace where you need, then cut it out and lay it on top. If you can't find anyone experienced with mylar it's much less risky than attempting the mylar yourself, especially on a rare game...

I'm not sure about PETG but both lexan and acrylic can be cut with a knife or scissors. You could probably even get away with just marking and drilling any relevant holes and lying the sheet over the entire playfield if you've already got it torn down.