Is there a personal preference thing there then or just some are bad?
Some can be quite bad.
Diesel tuning used to be quite straightforward hence the proliferation of add on boxes.
Being as they run at 100% airflow (no throttle butterfly or modern equivalent thereof) it was just a case of adding more fuel until the exhaust produced soot (unburnt fuel) then wind it back until the smoking stopped, check temps in the cylinder head to make sure nothing was going to melt and then market the result. A lot more complex potentially with all the emissions add ons now, plus the very advanced fuel injection/management systems but fairly similar principle.
With petrol turbos it’s more complex with ignition timing etc to take into consideration.
I’m sure a lot of the really cheaply developed maps just trick the engines into overfuelling and upping turbo boost forcing the ECU to try and play catch up making the extra power that way.
The likes of APR and REVO do put a lot of development miles into their maps which is reflected in the high purchase costs. The big timers invest a lot in advanced mapping kit and specialist programmers.
I’ve only used add on boxes on my earlier MK7’s due to TP1 scare stories but reverted back to standard in the end and my Clubsport I’ve kept fully original. Just a pedalbox is enough for these cars on the roads I drive.
With mk4,5 and 6 generation GTI’s and TDI’s I tried a few maps from different suppliers plus got to drive or passenger ride a few others.
REVO maps tend to be aggressive but they’ll offer smoother maps if you request them, APR seem very smooth and factory like in delivery just lots more power. Bluefin/superchips have a poor reputation yet don’t seem to struggle with getting customers, I tried a Bluefun map on my mk6 and it was much less aggressive and smoother than the REVO’d cars I had before it but noticeably down on peak power and torque. Not necessarily a bad thing as traction was never an issue and there were never any boost surges or flutter.
Aside from various tuning boxes I tried on my mk7’s I also got a good run out in a custom mapped mk7 R which was very impressive.