With the TUV approval the power gain is probably at thd limits of permissible emissions (higher output tuners have no such boundaries to consider) and simulated longevity tests with no appreciable drop in expected reliabilty. The unit shown there looks suspiciously like a DTUK Trevor box, likely same unit with different software for a mild output increase that probably won't cook the clutch. As much of a fan I was of the DTUK box for my GTD, I don't feel the manual clutch of the R and GTI have much overengineering to prevent clutch slip with typical box or remap increases - too many people reporting clutch slip. Is the DSG box more resilient or is it intelligent enough to tone the power down being put through it when too much?
Seems pricey for what it is, unless it comes with some kind of mechanical warranty policy.