No complaints from me for the DTUK box on my GTD and my dad continues to enjoy it in his, I did find the TDItuning one poor.
DTUK: Smooth, linear power delivery, no real life mpg penalty, slight over-read on the MFD mpg feels exactly like the stock map +30% at every stage of the throttle press, halved the number of DPF regens the car underwent vs stock. Off boost a tuning box will do nothing for you - don't forget that the old 2.0SDI (non-turboed) units only used to put out 75PS, the car will only have a fraction of its output off boost.
TDItuning: Harsh power delivery, not linear, induced wheelspin at 60mph in 3rd under hard acceleration (I feared for the longevity of my clutch), thirsty, induced twice as many regens as stock.
I have no opinion on the TMC system as I have not used it.
Some may "feel" the TDItuning box is doing more as you feel that kick, but don't mistake smooth and linear power delivery with a lack of response - take a look at how much quicker your rev counter and speedo dials are moving when you put your foot down without kicking 7 shades out of your clutch, and don't expect much difference off boost.