Unfortunately, when I removed it, I realized the massacre although "clipped", the shell does not prevent dust from getting between it and the machine. Since the Macbooks very hot, the compacted dust sticks ... Like the inside plastic shell, which almost melted in places, ending up stuck against the computer aluminum!
It took me several cleaning with alcohol 90 to get the better of most of the dirt that ended up stuck against the aluminum. So it is good protection ... Until we take it off, and here the damage is discovered.