I got pulled over last Friday on my way back from Laguna Seca and the cop stuck his head into my car. He didn't say anything about my GPS which is mounted on my windscreen (and also let me go without a ticket as I could convince him that not I was speeding but the red Ford Focus who blew by me and my buddy in front of me). lucky me
BTW: the law you cite would also make all of the "Fast Track" transponders illegal which about every 2nd car here has mounted on their windshields ...