Thanks for posting this--I've not seen it before.
It could be useful for macros and overhead shooting. I have an slr with an articulated screen and it's great for overhead and low, wide angle shooting. A mirror won't be as useful but is probably better than nothing.
My main reservation is the inability to easily detatch it. I suspect it's going to be in the way in normal shooting situations. They also missed an opportunity to allow it to flip upwards to shade the screen.
I'd probably spring for one for my LX3 if it were tripod-socket mounted, but taping it to the camera means it's there more or less permanently.