If the box has GPS
It will be useless in my car when the stereo is on.... for some reason if you switch the car stereo on any GPS device in range (up to about 1m from the car IIRC) loses lock. Tested on a stand alone GPS receiver bluetooth paired to a PDA, a Garmin Nuvii, HTC Desire (2 off), Motorola Defy, Sony Ericsson W810i
Much fun could be had switching the stereo on and off... more likely they would accuse me of tampering with the box :(