i looked into these about a year ago, but they come with a lot of risk, firstly the fact that you have it means theres more chance you will do something very silly, secondly i would be worrying weither or not it had spasedout and was up or down, thirdly if plod saw this on your bike, even if it was stationary, its a nick, and trust me traffic police know about numberplate flippers, i know of one person that has a flipper and he has istalled it so its very very difficult to spot and its activated by the horn button if i remember correctly and its even got another switch somewhere which shuts it down so it can't be activated by the horn, just incase pc plod are checking his bike, my biggest problem is i would be taking valuble concentration away from my riding trying to remember, oh theres a camera or i'm going to do a wheelie, i must remeber to do the flipper, because if your doing something silly chances are your gonna be doing silly speed, so the police will more than likely see you or hear you before you see them, so are you going to flip the plate every time you do something a bit unlawful....hmmmm
in the end i decided to go for a plate just a little bit smaller than normal and i'll keep my finger crossed the police officers eyesight might be a bit iffy
i do think they look cool tho, just not sure they're worth the risk.