I'm a little deaf in my left ear from bicycle-touring on busy roads. I'm not sure range/quality of this radar, but if it detects things that you cannot possibly detect, it could be at least a tiny bit useful. For instance you are riding into headwind down a windy one lane dirt road at night. If I car is trying to pass you at the 20 mph speed limit that's fine, but if some joyriding kids are "offroading" on road at 30-50 mph, they aren't going to be able to stop.
Sure if you hear them you will get off the road and try to take a picture of their license plate to send to the police, but what if the conditions (wind, EV, something else) are such that you can't hear them?
The device will tell you *when* and at what speed the vehicle is going to pass you, which are good bits to know in certain circumstances. I don't know about carrying the extra weight and charging the batteries for the thing. If it was small and I only had to charge it once a week though... I would put one on my bike.
As far as the LED blinker application... Good LED blinkers are highly visible and make you safer. I don't see any value in varying the frequency/intensity of light/type of blinking for different speed drivers. If you are riding at night or in the rain or other poor visibility conditions, you should have your LED blinkers on at the highest setting. You don't need radar control for it.