Saw one of these once stuck on the top of an RT screen. Its like looking into those trick mirrors in fair grounds. Very difficult to work out were everything is coming from and at The same time giving you a big blind spot in front of you. I'm amazed their legal.
A lad I knew had one on his bike a few years ago. There a couple of issues said to be annoying; one is if your wearing a high viz jacket your own reflection can be very distracting, and secondly if the sun is behind you (or even at the side) it dazzle's you relentlessly.
I was born with nothing and unfortunately I still have most of it left.