I would never pay £800 for radar cruise control but our latest (used) CX-5 came with it fitted as we specifically wanted black leather. I can find no other review on here so here are a few thoughts.
It is un-nerving to use at first as it will follow the vehicle in front down to a standstill in heavy traffic (as un-nerving as driving into oncoming traffic at night on full beam). A touch on the accelerator and it picks up speed accordingly. All very good.
What I do not like about it is that if one is cruising at 70mph (say) and has to keep behind a lorry doing 60mph it will career up to the lorry at speed and then brake noticeably before keeping a fixed distance behind it. With standard cruise control I would cancel well before reaching the lorry and ease gently up to it.
Worse than that though is that, if anyone drives across you, it will slam on the brakes well after the danger has passed, irrespective of whether or not the car behind will crash into you. This happened twice on my first journey! There was a car parked on the shoulder where two motorways diverge and I took the left one. Presumably after consulting a map, the parked car decided to take the right hand road so crossed three lanes ahead of me to get on with its journey. Very heavy braking.
Then, later on, I was following a recovery vehicle at speed when it saw the vehicle to be rescued in the shoulder so it suddenly pulled left in front of me to stop by it.
Each time my car slammed on the brakes for no real reason. I can imagine it might do this too, if a car drives at speed down the fast lane and suddenly pulls across the road to take an exit slip road at the last possible moment.
One interesting feature is that the new cars come with “auto hold”. This is a button similar to, and next to, the electronic handbrake. When depressed it stops the car from “creeping” forward in queues so there is no need to keep the footbrake hard down and the person behind is not troubled by brake lights. Interesting and useful.