Do you have the basic head unit? The business cd?
If yours is the sat nav version, I dont have knowledge of that one.
I replaced mine a while ago and don't regret it.
The cars time is still setup on the main instrument cluster as per normal. I think the new radio time is separate but can't remember.
I had to get a harness for the steering wheel controls but apart from that it was fine.
The only other feature that I can think of that I lost was the auto volume control where it adjusts according to your speed.