I had a Dension Icelink Plus for about 2 weeks- worked great with my Concert stereo but then I upgraded to the RNS-D sat nav unit and it started playing up with that.
I now have the Kenwood Media Unit which accepts almost any input source-USB, phono, Ipod, 3.5mm etc. and you get the track info on the display which you dont on the Icelink.
If you are going to go for it, I would buy the Dension Icelink and not the Audi unit- basically the same thing but with the Audi one, they have disabled the controls on the IPod whilst it is docked. The Dension unit does not have this restriction- I have tried out both.
Ebay has very cheaply priced units. I got mine from a Canadian seller; about £50 inc p+p.