I used to have a DTUK box on my early MK7 Golf GTD (184ps 2.0TDI CR DPF).
On paper takes it to same 240ps/500Nm, never denied, but it was great. To put it in easily imaginable terms, with the box on, the car pulled 6th like stock power pulled in 4th.
I agree that mpg gains are total ********, under-reading because the car is using more fuel than it thinks it is, but as the DTUK maps don't lazily put in an arbitrary overfuel across the board, the readings with the DTUK box are close to stock readings as under low/med throttle, overfuelling isn't silly.
I actually saw my DPF regens half that of stock on my favourite setting of 2:1, but increase on setting 3:3 (huge overfuelling at the top end, but without any real performance gains.
I measured my performance gains on a slipriad onto a dual carriageway and see the speed I get to at a certain sign past my rolling start at 30mph, I compare all my cars like this. My GTD hit 81mph stock and 88mph with box.
Prior to the DTUK box I had a TDITuning box on my GTD, which was atrocious- crude and massive overfuelling at every throttle input - put your foot down, get wheelspin in 3rd at 65mph and mpg over-reading by 20% and DPF regens very frequent - avoid TDITuning.
Seriously thinking about getting a DTUK box again. My GTD was a manual and the clutch coped with the extra power/torque. The A4 is DSG - do stock clamping pressures on the DSG clutches hold with 240ps/510Nm or will I need a DSG remap?
My Dad's DSG on his Golf GTD held up, but that is the 6 speed variant, not sure if the 7 speed box is more sensitive or delicate than the 6 speed.