I tried to use my Garmin radar without a light on tour several years ago. The battery could never last through the day. Maybe newer units have a better battery life. I don't even use mine anymore in an urban setting. I find my ears generally give me the info I need when I need it. If I were severely hard of hearing I would place much more value on the radar. I seem to be an outlier, though. Most users seem to rave about them, though I haven't heard much from tourists. I rode the GAP and C&O trails this past summer and one of my partners was using something. I can't remember if his had radar, lights and camera all in one or if there were two different devices. He was having battery issues with something.

I don't remember any false positives however if one is riding a frontage road, the radar will likely pick up vehicles on the parallel road. Important to keep in mind the radar is detecting a faster moving object. If a vehicle slows to your speed, it will drop off the radar but still be there. One needs to be aware of that. When on a multi lane road, the radar can't tell you which lane the vehicle is in, at least mine can't.