I bought the BT integration from VW when I bought my car, and I found it lacking. I have a Komfort, so I don't have any steering wheel buttons, but I still expected more out of the integration.
PROS: The installed mike next to the map light buttons works well, even with the top down. You can hear the caller clearly, and they can hear you. When a call comes in, the radio mutes, and displays "phone active" or some such thing.
CONS: A big one-- you can 't answer the phone by hitting a button on the radio. You have to fish the phone out of your pocket and hit the button to answer.
I knew that, without steering wheel controls, I'd miss out on some functionality, but not being able to answer the call without handling the phone is huge drawback. And it is even worse, now that I've switched to an iPhone, which is hard to answer by touch.