My suggestion... if you're going to be doing a lot of highway driving, don't waste your money.
My company provided some equipment for a police conference and there was a session about technologies related to speed enforcement.
Not going to do you a single bit of good on highways because if a State Trooper is measuring speed, he's using laser to do. While just about all the newer model detectors advertise that they "also detect laser", if it does detect laser, you're already dead in the water.
The benefit about the older style radars is that they threw off a lot of stray signals and radar detectors would pick those strays up nicely. Not the case with the laser guns. Lidar (laser guns) has a beam that's something like 3'x3' up to 1000 yards away and they can pick you off from a mile away, while providing a measurement on speed and distance in under a second. By the time you react to the detector signaling, the trooper already has your speed and made a decision on if he's going to pull you over or not.
This video is an interesting example of the laser gun in use: