Erm, I think Radar detectors are a good idea, and one is on my list. I don't really hoon or speed, but let's me honest, some of these cameras are sneaky as fuark.
Also, I've nearly rear ended people so many times, when some one panic-breaks after seeing one too late, so having some kind of system to alert me of that, so i can prepare for it makes sense.
That being said, the cops want your money, they're not going to like the fact that you're messing with them.