I think it's standard equipment now, but I know when I ordered my current GTD early 2016, it was something like a £150 option, and if you didn't select it then late 2016 builds could have it activated as you say via a registration code available from the dealer.
Is it any good ? We'll for me yes, but your mileage may vary. I tend to listen a lot to my in car music on either Spotify or particular web radio stations via tune in radio (which I tend to listen to by Android Auto). Works very well for me and gives me all the cover art / track info etc. and looks nice.
I know you can do these via bluetooth but for me that's a bit more faf. I also really like the Car Net and find it really useful for Petrol prices and car park locations when traveling.
Suppose it all depends on how much money they want to activate it, but I'm glad I ticked that box.