This isn't for city riding. It is for riding on country roads. If you've ever done any road cycling outside of city centres, it can get very risky as the cars are going so much faster and there isn't the same road shoulder. Your ears are not enough. Personally I hate cycling on country roads because of this so I would definitely use this radar.
I agree with an earlier comment about non-visual feedback. An audio queue would be good (thinking like the trackers in the Aliens movies)
Most of the country roads I cycle along (even the ones shown in the video) have enough curves that by the time this device detects a car you would be able to hear it.
Even then I'm not really sure what the point of this device is. If a car comes speeding up behind you what you are supposed to do? Pull over and stop? Drive on the edge and get covered in mud?
Most of my riding is this, and I think the risk here is perceived risk, not actual. Generally getting smooshed from behind is a low-likelihood event. When it does happen it's on fast trunk roads (pretty nasty to ride, but also usually avoidable).
This looks like another techy boondoggle to reassure people. Cycling is littered with 'em.
I have been in a number of driver at fault cycling collisions. Although I was never hit from behind I have had 3 near misses by cars going over 40 mph. It isn't a low likelihood event.
I agree with an earlier comment about non-visual feedback. An audio queue would be good (thinking like the trackers in the Aliens movies)