I tried one, but it's only convex in one dimension, and, for some reason, even though I could technically see everything in it, it was hard to get my brain to comprehend the horizontal image quickly. I have no explanation for that, but it just didn't work out for me.

I really did want to get a rear-view mirror, though, with an arm that I could have adhered to the shelves at the top of the cube. That would have cooool. (Or maybe that should be that be k-rad, d00d.)