This is true. If following a car doesn't require a warrant, then using a gadget to do so shouldn't require a warrant either.
Just goes to show, government efficiency is a catch-22.
And if a cop follows me around for a week, I can rightfully have charges brought up on him for Harassment. This is also no different.
Another issue, GPS signals are extremely weak. They must have a skyward view. You can block GPS signals with a piece of construction paper, so this device must have a visible antennae or it's going to be useless. A device under the bumper, in the wheel well or on the undercarriage isn't going to record much of anything.