I'm assuming that you are asking about the ScaleTrains TM X-large-knuckle couplers (McHenry lookalike), not the MTL clones ST has chosen to use in some of their more recent models.
The Scale Trains "boxing-glove jr." McHenry's cousin is much chunkier looking than MTL couplers. It goes totally against Scale Trains' goal for making accurately scaled models. MTL couplers also couple with much less effort than ST couplers.
If you are asking about ST's MTL clone couplers, I don't own any of those so I cant' comment. But going by my experience with other MTL clones, none I have encountered live up to the genuine MTL's performance. They are not molded as well as MTL, they don't use reverse-draft-angle molds, and the springs are often too stiff.