I've seen quite a lot about this on TV, especially Mythbusters.
Some people see speed cameras and revenue raising devices, only there to hit you back pocket, not doing much at all to reduce the accidents. They tend to make people pay more attention to the speedo instead of the road.
Mythbusters have run several episodes where they have tested devices that are supposed to either make it difficult to read number plates or confuse the radar unit. Some of these devices have actually been legal but most have not. None of them have worked.
I have a sure fire way of ensuring that you never pay another speeding fine, never get caught by speed cameras or any other speed detection device. It's quite simple.
DON'T SPEED! EVER!
Simple as that.