The base of the mirror is not large enough to cover an old work electrical box. This is the only way to add the mirror to a wall. I'm not sure what they were thinking.

Perhaps they anticipate you installing the mirror over an existing outlet with a new work box. That's the only way this would work.

It's a darn shame. The mirror seemed nice, but it had a huge glaring problem. Not sure how it made it out of R&D like that.