Originally Posted by markk

I thought it was CANtcu that used the OEM tcu.
If you are big power though you are then stuck with the BMW protocol for operation and might need the ability to make changes.
If you were pushing less than the factory car then no issues.

For example, 8HP45. Small enough gearbox, but will only handle 450nm. That is the safe design capacity from ZF to warrant the box.
The box itself will do 550-600nm but the safety protocol won't let it.
The systems that bypass the oe tcu allow you to exploit these 'extras'.
Or you go big and fit the one that suits your torque range.
Oh and the 8HP don't like much over 8000rpm.