I'm having difficulty in appreciating what benefit a rider gets from a radar that tells you about an approaching car.
Do you really think you'd be able to "get out of the way" if a car was about to hit you from behind? While having advance notification of a collision might be interesting (for that brief moment while you're still upright), I can't imagine this being terribly useful once the collision has happened.
I can think of situations in a group ride where this would be super-handy to have, where you've got other bikes close behind and to the sides and back of you.
But as a collision-avoidance device, or pre-collision awareness, I don't understand the usefulness of that - especially if it's not recording anything. But I could be misunderstanding the purpose of the device. People here do seem to really love them.