I am not a fan of these keyboard covers. Because they add to the mass of the keys, it may cause the keys to press up against the screen when its closed and damage the screen.
This happened to me on my rMBP, what basically happened is there was white looking smudges in some parts of the screen that wouldn't come off. It was from the protector. Never again!
Luckily, I had an unrelated issue which was fixed under AppleCare not too long after it happened and they replaced the screen while they were at it. If it wasn't for that, it would have driven me crazy!