I heard a story once about someone who had one of these
black boxes installed in their cars because they let their kids drive it. They were driving like normal, through a school zone, I think it was 35, when a cop pulled them over and said they were doing 55 or something. Normally this would be a huge ticket and a lot of points, but they had this box proving that they didnt go above 35 so they got off. So, this proves a point - cops are not always right, but you have no way to prove it unless you have something like those speed monitors. I don't worry about it too much myself, and I suppose the evidence could also be damning, but it could help you out in some situations!