I'm one of the few (maybe the only one here) who has tried both. The TDI-tuning box had a savage delivery of power, rough idling and lumpy performance that saw me able to spin the wheels in 3rd at 65mph when I put my foot down. I had more regens than normal, and my indicated mpg became 16% optimistic. All of these points lead me to believe that the TDI-tuning box massively overfuels when you put your foot down. I was not impressed and sent mine back.
The DTUK box on the other hand is smooth and progressive, delivering linear power increases, no rough idling, less optimistic gains in MFD indicated mpg (9%) optimistic (vs 3% optimistic without a box), and dyno proven gains you can see on the website. It was handy being close to DTUK for a personal visit to the place to try out the goods, although that won't be possible for many. No wheelspin in 3rd at speed means more usable and predictable power. It feels like stock with a 27% gain across the range.
No contest for me, DTUK every time.