The little bit of experience I have with it only shows that it is a different coating. Nothing better, nothing worse, just different. I did hear one guy saying how he had it on his hip for 3 days of rainy training, and it had some LIGHT rust on the side of the slide next to his shirt. He also said it rubbed right off. (I don't know if that was from the gun or from the holster or anything else.)
I like them because they are different, and you used to be able to find one for the same price as a regular glock in the stores. BUT, the last one I saw was at a Gun Show for $700.00!!!!!!
Supposedly, the EXO technology does not require lube. Thus, nothing for sand/crud to stick too, making the gun operate smoother in tough conditions. I have not had personal experience on this part.
In summary, cool factor up because it is different. Indifferent on everything else. That is about an objective review I can give with the little experience I have had with an EXO Glock.
I have a FailZero BCG in my AR, and love it. It is true that if they put a thin layer on it it will polish off with use, but a true thickness adds to the hardness of the metal and makes it harder for carbon to stick to it. I have seen entire AR's and AK's that have been coated and it makes them last almost forever.