Hi BTS,
There are some differences between gnexlab extruder controller and the makerbot's. The main issue is gnexlab controller is standalone and do not communicate with pc. The on board lcd and trimpots let you to set the extruder and the heated bed temperatures. If you want to use mach3 as a 3d printing software, communicating via pc while mach3 pulsing the motors become a problem. The message traffic corrupts the pulse sequences. The gnexlab solution lets the mach3 control the motors including the extruder stepper as 4th axis. The gnexlab extruder controller dealing with the temperatures without pc.
Regards,
Nuri Erginer