Looking At it another way, as I find it easier to explane....
Take a 2015 with screen and telematics. All 3 are "paired" using the security code and tech2.
If you depair the telematics you then have 2013 software on your 2015 head unit. The print on the facia is the only hardware difference, while the software changes the red and green phone buttons function to "home" destination on the sat nav.
The problem you 'll have upgrading to 2015/adding telematics is the loom plug won't be present, and the unit all but fills the glove box. Blutooth is a far easier answer and arguably more convenient.
Having said all that it is possible to have the loom plug added, and hence the telematics unit relocated to e.g. the boot Bose shelf/first aid cupboard/Carin cage.
CID as a good enhancement over the GID. It's more clear and makes the software easier to use. Recommended!
But as said, any CID unit purchased for retro fitting MUST MUST MUST be depaired from it's original head unit, and hence in DELIVERY MODE in order be usable! Otherwise it is useless.
Steering wheel controls completely replace the stalk buttons btw, which are no longer needed. Takes a bit of getting used to, but it's far better IMO. Be aware In some modes some steering wheel buttons have no function.
