I tried one of those a few years ago and took it back out. It worked very poorly. Only OK at just the correct view angle, if not the right angle they do not show up well at all. Maybe they have changed. The concept is good.
I saw them in some Harleys while in Daytona this year. If you're dead on in back of them, it shows up OK. Not great, but OK. If you're "off angle" I didn't think they showed up well at all. My 2 cents.........Don B