I've worn a Mii Mask for only a few seconds. I didn't know what the make-up option meant, so I tried it. It scared me so bad that I thought I had somehow broke my game and I hurried and shut it off. Ever since then I've never made my character wear a Mii Mask. In my opinion, they don't fit in with Animal Crossing's atmosphere.
Never liked the Mii Masks at all. They don't fit with the player bodies and the aesthetics of Animal Crossing. I once tried one on and ran around seeing how horrible my mayor would look against the town and villagers. Needless to say, that experiment won't occur again. The only time I'd wear one is if I was purposely making a character look horrible.