I just picked up a zagg glass last night at best buy. I bit the bullet and paid the 8 bucks to have them install it, as if they do I can take it back there if/when it gets scratched and get a new one put on no questions asked. It's pretty much the only thing I'll pay their price premium for, as it's not that much more and it's infinitely more convenient. Also, zagg charges shipping, and some people are claiming they also make you pay 15 dollars every time you get a new one as well. So after the first swap, I'm coming out ahead.
As for the protector itself, it looks amazing. It's crystal clear and I think it actually has a better oleophobic coating on it than the stock screen does. It barely figerprints, and they are incredibly easy to wipe off. On my m7 (I have the m8 now), 2 days after I got it I cleaned the screen and managed to get a piece of sand under the cloth and put one hairline scratch in the screen. It drove me nuts, and I was worried every time I wiped this screen down the same would happen. Now I can rest easy. I definitely think they are worthwhile, and the zagg seems as good or better than any of the rest.