not wanting to get into an argument about it but I have had a box on my d5 for 2 years now and approx. 16000 miles, no limp mode, no dpf issues, no gearbox issues only issue was I wore out a set of pads and discs but that was on the list to be done anyway.
I never reset my average mpg either and went from 30mpg to 35mpg (all the dreaded short journeys) in about 4 weeks. then went from Liverpool to loch Tay still without resetting my mpg and had got upto 48 average mpg by the time I got there. I was not hanging about either. funnily enough that's over 2 years without resetting my trip computer
admittedly though the box was supposed to be temporary as it was an expensive piece of kit that I got hold of second hand cheaply.
my new t5 will be remapped.