Personal experience ,
Diesel power box : increased torque low down, much nicer to drive, fast on the motorway, surprise a lot of people, 2mpg worse...wrecks clutches, makes them slip due to high torque low down...
Remap : tuned to @140bhp, best option, tailored so not so much torque low down, better for clutch life, but overall more powerfull, very nice to drive, mpg about same, do not want to go back, engine seems ideally suited to multi, fast, smooth, dark horse...
Tempted to do mine, but will have to wait until I've replaced the Clutch (tomorrow) . . . and done the trailing arm bearings . . . and the ARB bushes . . . and finished rebuilding my Bikes . . . etc, etc
It'll be like a new car, they may even map it for you, and if you are not happy, put the old map back on, with no or small charge for mileage, it doesnt take that long to do.