I actually just got and installed this crystal protector. The reviews aren't the best, but I've had a good experience so far. It's not big enough to cover the entire crystal, but that's because the crystal is slightly raised and curved at the edges. I'd be more worried about the face of the crystal anyway. It's absolutely invisible once installed. I sprayed a little bit of an alcohol + water mix before installing, and it worked perfectly. It will need a little time to dry, but then there should be no air bubbles.
Let me know if you have any questions!