At the beginning of this guide, it was hinted at that this technology almost seems like it would be illegal. Well, in most states, cities, and provinces it is legal. But, there are certain locations around the world where this technology is actually prohibited. For example, there are some provinces in Canada where it is illegal, as well as in the entire state of Virginia.
As to why some locations prohibit the use of them, some believe that they encourage speeding and general reckless driving. Others may also feel like they are a distraction to the driver.