A JM press is like the good morning equivalent of the bench press.
It’s almost like you’re emphasizing ‘bad’ positioning on the bench press.
In a regular bench press, you want the bar, your wrist, and your elbow in a straight line perpendicular to the ground. Sometimes, people will let the elbow travel in front of the wrist and bar or the wrist/bar will travel behind the elbow or some of both and this puts a lot more tension on the tris and elbows while taking away from the chest/shoulders/etc.
So with the JM, you’re intentionally committing this ‘error’. With a good morning, it’s kind of like a squat gone bad where the bar gets forward of the center of the foot. That’s why I liken them to each other.
When you think of it this way, it isn’t at all that complicated a movement and I feel it’s much less technically demanding then say dips where there’s a lot of different compensation patterns that can occur that reduce both the effectiveness and safety of dips.