I have just recently fitted a tuning box on my 525d sport (2005 with 80K), the make of the box is Drake box 2 from Italy.
It's defiantly impressive, increasing BHP from 177 to 225ish! and MPG from avg: 35mpg to 46mpg. everything seems normal, engine temp idle RPM.
Does anyone have any positive or negative experience with tuning boxes? can they do any damage to the engine short or long term?