I asked the same question about 5 months ago before ordering mine.
I too had tested the TTS with it on and was quite impressed.
HOWEVER. I had an S3 sportback for the weekend with it on, and I'm not sure what it was, maybe the extra weight of the car I'm not sure but, when it was off it was just like it was when it was turned on.
In fact I then asked to use a non Magride car and the ride was so much better I can't even begin to tell you. So, I ordered mine without it and saved the 900 quid.
Great on the TT, not great on the S3. I'm thinking they should have put the "audi drive selct" off the A4 onto the S3 instead.
Hope that helps.