Your already using MHD so why piggy back the jb4? I think you should get rid of it and do as the other guys are saying. Custom tunes with just MHD. DOC can def get you up in HP.
a lot of people saying that, and yes should be better since you skip a step of communication.
dealing with a local tuner, the guys sees numbers, and he stated the difference are not huge power wise, and how the car drive.
The main issues is the 'single point of failure'' added in the system. More complex, more wires, many options to mess with, etc.
Reason people using it, is because they already had this, and meth. Also user adjustability can be done on the spot.
Right now on my side it's working very well.
BUT, yes, so many forums comments like that want to make me change it to MHD only one day
However, MHD liscence + new meth pump controller + new tune = not cheap. around 1300-1500$ cad.