I think its the manner in which you skin the cat that's important.
It looks like some tuning boxes just spoof boost, so in effect, just obtains the increase in performance simply by increasing turbo boost. Sometimes this has knock on effects, for example, snapping the throttle plate shut may cause compressor surge etc., or drivability issues are certain loads or speeds.
The MTM box and harness looks to be connecting more sensors, so potentially this is a more sophisticated box, but without the details I can't say for sure.
A true ECU remap can/should be a more sophisticated solution, where you can vary many more parameters, eg: fuelling, ignition timing, injector duration etc. so is seen as less of a sledgehammer approach than just keeping more boost in.