While it may not be illegal, it will guarantee that you get a ticket. I have several friends who are cops & every one of them has told me that the second they know that you have a radar detector, they are going to hit you with the full penalty & then take a look over your vehicle for any other infractions they can stick on you.
I have had radar detectors by three different major brands. They all worked fine, but I still got pulled over with all of them. With the instant on laser technology they have now, you cannot know ahead of time if someone is gunning you, and by the time your detector goes off, it is too late.
I have completely gotten rid of my detectors & I just make myself more aware of my driving. Try to keep your speed within 10 MPH of the posted limits & you should be fine.