I have used a few over the years, the best one for me is the Brabus on my Mercs and the CRD2 and CRDT+ from here...

Diesel Tuning UK | Select the right tuning system for your car

Some just over fuel, some adjust fuel and boost pressure, some do fuel, boost pressure and injectors etc.

I have had better results from boxes than remaps, but only when it does boost too.