Doesn't it only work if everyone has one? If only one or a few do, they can be as cautious as possible and still be the victim of another reckless driver who doesn't have one. It reminds me a bit of the trend where parents buy larger vehicles for their teenaged children because of their perceived safety. It ends up having the opposite overall effect because less experienced drivers are getting into accidents with larger and more deadly (to those around them) vehicles.
I think it would work for anyone that had one, even if they were the only one, as they would be a much more defensive driver. They would probably save money on gas as well :)
