I had them and have installed many. I donno about other states but In wisconsin you can not drive with any on. As long as your car is parked then the cops cant do anything other than ask you to turn them off, if your in a busy area it can be kinda distracting. But i guess thats the point kinda.
You would think that noens wouldn't have any laws against them since it increase peoples awareness that your there. Not in the, "hey, who's that" kinda way but, like "if that guy didn't have a noen, I would have hit him" or something like that...
I forgot to add this from above but, are there any laws of having noens on inside your car? Like if your amp had a noen on it and people outside your car could see it, would you get pulled over for it?
And won. (Nevada)