Tuning boxes, which plug in between the rail pressure sensor and the car's harness, only really modify the signal from the rail's sensor in order to cheat the system into raising the rail fuel pressure and similar for turbo pressure. No all boxes modify the boost pressure. There are more sophisticated systems that plug into the harness between each fuel injector and these can alter the duration and timing of injection as well as fuel pressure. Steinbauer comes to mind as a company that can supply both types for many engines.
https://www.steinbauer.cc/gb/products/
Mapping is more effective. However many ECU's [most even?] can no longer be simply flashed with a modified engine map that overwrites the original. In many cases the ECU has to be opened and the chip unsoldered and removed to be flashed, before re-soldering and closing again. This is not a trivial exercise. Not sure about that that box that fits on the OEBD socket inside the passenger's compartment. It's an intriguing concept of which I have no experience whatsoever. I have used tuning boxes on various cars and plant equipment and they work well on some, hopeless on others and pull up error codes on the dash of yet other vehicles. I also mapped my Q7 and it was brilliant. It transformed the performance of that car in a very positive way, bringing the performance up to equal that of post-facelift vehicles with the more powerful factory engine. It did actually improve fuel economy slightly, but not by as much as indicated on the dash display.
Personal opinion but I would be more inclined to risk one of these on an engine that was not already at the top end of power output for that engine family. That means I would maybe try it on a D4 but not on a D5.
I have got Polestar on my XC90. The power output hardly changes but the gearbox map does. Yes it is noticeable, for the first couple of days, then you forget what it was like previously, which was perfectly good but slightly different. Polestar is about to make available a new version with 'overboost', which is a temporary, 15 second approximately, serious increase in power. Useful for overtaking up hills one supposes. This is also apparently being offered as a free upgrade for people who bought Polestar in 2018 and makes the Polestar upgrade look like much better value for money than it was. More bang for the buck.