It helps when the car is going real fast so you don’t even have time to hear it or for people who don’t want/can’t look behind them to know if there is a car when they turn left.

With a radar you are never surprised so it can help some people to feel safe.

I don’t think it changes how you react but how you anticipate.

Even then I don’t have a radar on my bike. It’s too expensive for my use case right now.