Tuning Boxes - What have you got and what are your findings

[ozzopel]

Purchased a DTUK box for my 2.0 CDTi J shortly after buying the car as I was so disappointed with its performance compared to my 1.9 CDTi H.(both manuals). Did not install it until the car had travelled ~7000mi. Left it on factory settings for 15,000mi, there was not that much difference to performance on that setting but had to remove it as the clutch began to slip on freeway @ 70mph when I planted it.
Now I'm not sure if the box was the problem but the clutch has not slipped since it was removed. Odo now at 37500mi