I take it you haven't tried it.

Nothing says it has to be your only tail-light. I use it along with a Cyglo-light.

I find the radar completely indispensable, especially when going down-hill and in other places where a car can sneak up by surprise. No, it won't tell you that someone is out to get you, but it helps remove the element of surprise.

I have the version 1. The version 2 has a better light. I use both it and my Cyglo-light in flash mode for daytime riding. My one gripe is that it has to be mounted on the seatpost. I have short legs, so not much exposed seatpost, and it is a tight squeeze to get its mount and my saddle bag on. (There would not be enough room for version 2). When I have a rear rack on, I can mount it on that (I bolted an extra 1/4-turn mount to the rack where most people have a reflector.)

The only time it doesn't work is when a car is following me at about the same speed I am going.

I used to ride with it and a mirror, but I have found the mirror to be superfluous; a head check is much more expedient and dependable (I break helmet mirrors frequently.)

In heavy traffic areas, I find it annoying, but on country roads, it has really improved my quality of life.