So far I am loving the changes.  TCU: The shifts are smooth and fast up and much earlier downshift points.  The TCU upgrade is critical as it allows the transmission to match with the APR map.  I think the pair is a must and should be considered mandatory.  ECU: This is a great motor and APR makes it better in every way.  Power is delivered quicker and with greater force, especially when the throttle is over 50% down.  The engine winds up fast and triple digit speeds are there in a flash.  Passing power will suck you into your sport seats!
If you like your S3 but want to see what 357HP and 366TQ feels like, I recommend it.