Using a torque meter is indeed beter for all systems because you will use a universal standard scale which will not be different among several different products. I know many years ago there was such a torque tool to measure offroad diffs Never know what hapened with it but it probably wasn't a succes or too expensive.

This is only to compare and if you use the same tool and within the production all the same spec materials (basically the motor) you can make it a setup option to note.