Just installed a sheet of Invisiglass from CoinTaker on my JP yesterday. The edges were square, but the coating appears to be on both sides. (They feel the same, have the same appearance) I searched for instructions, but didn't find any. I put the etched label (very bottom corner, easily hidden by the lockdown bar) facing up. I had a few friends over to watch a movie in my theater. An unsolicited review was given by my friend's 16 year old son: "I tried to touch that can of Barbasol (Mezel Mods) , and was surprised when I hit glass!" When I told him that I had just installed it that day, he said, "I'd say it works!"

I bought my 2 pack of Invisiglass here. I've been very happy. Several people have thought there was no glass on the machines. It's a very quantifiable improvement that I think is justified at this price point.

This and a microfiber cloth is what I use to clean it:

https://www.walmart.com/ip/Invisible-Glass-92166-Premium-Glass-Cleaner-22-oz/16879959?wmlspartner=wlpa&selectedSellerId=837&&adid=22222222228017003432&wl0=&wl1=g&wl2=m&wl3=42978140072&wl4=pla-81470382992&wl5=9016919&wl6=&wl7=9016910&wl8=&wl9=pla&wl10=112343835&wl11=online&wl12=16879959&veh=sem&gclid=Cj0KCQjwvb75BRD1ARIsAP6LcqvdFrQdRDNuiCOTkakLDn-K0R_mHAaAS_G9rrzJlKiuiMAn0QVTeHsaAjrnEALw_wcB

It feels like it's coated on both sides. I usually put the logo side up, at the bottom right corner.

Put cup holders on. Even with regular glass, I can't imagine a person placing a drink on one of my pinball machines. These are adults you speak of, right? I'd definitely be worried about keys scratching the coating, though in the trough area it probably would not effect gameplay.

I now have Invisiglass or Voodoo on all of my games. If your collection is too large to do them all, or all of a category or section of games, don't start. You can't unsee the man behind the curtain. It's best to not know he's there.

Stern sells their own branded "HD Glass." I've seen it installed on machines, but never handled it for closer inspection. I haven't seen it in stock anywhere for quite a while, and it is typically more expensive than two other options.

Voodoo is only sold through Cointaker, to my knowledge. They also typically sell Invisiglass, which is what came from the factory on my Wonka LE. I have 5 machines, with a mix of Voodoo and Invisiglass. They both look so much better than regular glass, and once installed, you would have a difficult time quantifying the difference between them. Invisiglass has a slightly better finish on the edges, and seems very slightly easier to clean. I had one piece of Voodoo arrive with a scratch (that was promptly replaced for free) and feel that it is slightly more prone to scratching than Invisiglass. We are talking Vanilla vs French Vanilla here though.

TLDR: by whatever is in stock and on sale. Cointaker appears to have both right now, I'd buy a two pack. If you don't have two machines, sell one to a friend and split the shipping cost. Keep your factory glass in the new box, and never sell a machine that came with standard glass with your upgraded glass.