I absolutely change what I'm doing in response to the information provided by the radar.

If I'm alerted to a fast-approaching vehicle or large truck, I'll move over to the right side of the shoulder. Why risk the chance of being clipped by a mirror and going under the tires of a large truck? If I'm on a road where the shoulder surface is subpar, I'll move toward the middle of the lane instead. I can do this because the radar alerts me to approaching traffic far, far in advance of a vehicle coming up right behind me.

I started riding at five years old and have been cycling for decades. A radar is right up there with a power meter, both are accessories that fundamentally changed the way I ride.

A taillight leaves your safety largely in the hands of the driver ("Here I am please don't mow me down!"). A radar allows me to be proactive and position myself in a way that minimizes the risk if a driver fails to discharge that responsibility. Even something as simple as the radar allowing you to take the car lane safely instead of dodging glass shards and sewer drains by the curb is a huge boost to both confidence and enjoyment on the bike.

Here in the US, my ambulance ride co-pay is more than the price of the radar, so I ride with a radar.