It plugs into the fuel rail sensor at the back of the engine and then the boost pressure sensor at the front of the engine (on mine anyway. Location will be different on other engines).
The loom then connects to the Tuning box which intercepts the signal to the ECU and alters the boost and fuelling accordingly. So similar to a remap (before people start the remap vs tuning box argument I know there is a lot more involved in a map!)
The difference with this is its easy to remove yourself. A remap you can't.
To be honest it has surprised me at how good it is. There are 28 different settings on this particular box (4 different maps with 7 power setting adjustments for each map). Yes a remap would yield slightly better results on a Dyno and be less "crude" in how it achieves those results.
But for something that takes 15 mins to fit and remove it's a no brainer.
As for the best way then that would still be a remap. There is a company called GAD Tuning that have tuned a C350 CDI to 340bhp and 800lbft!!! That's with remap, EGR switched off , DPF Delete and a larger bore TBE.
Mine now has around an extra 40bhp and 80lbft. Which I'm happy with as I just wanted a bit more shove. I don't intend doing anything else after I've found some better air filters (which is proving difficult at the moment)
