I am on my second car with a Superchip (both diesels). I have nothing but praise for the results and the service I have received. I deal directly with the Head Office in Buckingham.
The work is backed by a warranty. I am not aware of any recent issues with stories circulating about problems. Historically, I am aware of dissatisfaction with individual dealers, and I think the development of software code being flashed into the ECU rather than having to open the unit and solder a new chip has eliminated "physical" risks. The company has been at the forefront of its industry since the infancy of ECU's.
Other companies may claim to achieve higher power gains. Maybe they do? Having been in a variety of tuned cars now I am still sticking with Superchips and have read over 2 years worth of threads on this forum about the relative merits of each tuner's offerings.
When over there, I have invariably seen a VW Racing UK car being worked on, such as the Rcaing R32 and MkV diesel.
I would say to him don't rule them out. If he's local to you, he is not so far away that he can't pop over to Buckingham and ask questions. He would also be near to REVO (Northants?) and a return trip via Jabba in Peterborough for a comparison.[