I have it on my 2012 Focus, it was never mentioned when I bought it, so the dealer probably didn't even know what it was
In short, it's fantastic, and makes ordinary cruise look soooo last year.
As said above, it tracks the vehicle in front, keeping the correct distance, and will even slam on the brakes when some t**t in the next lane cuts across in front of you. It probably works better with an autobox, but on a manual, it tells you when to change down when slowing beyond the torque of the gear that you're in. If it slows you to a stop, it will go into standby.
It does have a couple of "quirks" that need getting used to; one being that if you're on a multi-laned road, and starting to creep up on a vehicle in the next lane, if the road starts curving across you, then the radar will "see" that vehicle as if it's in front, and slow down appropriately. You then need to override the cruise, or switch to a lane further across. It's fine once you get used to it, and because of the way it works is so much more useful than standard cruise, which I used to get fed up trying to use on a busy motorway or trunk road.
The reason that its so expensive is due to the radar unit which allegedly costs around £700 just on its own