The radius of the dumbbells gives the effect of a board press, which limits pressing range of motion. Specifically, shoulder extension is limited. Individuals with certain shoulder injuries, such as functional anterior instability, may not tolerate loaded shoulder extension. Hence, the hex press may be a suitable option.  Diving deeper, functional anterior instability is thought to be related to decreased activity of subscapularis — a muscle of the rotator cuff. (4) Squeezing the dumbbells together at the bottom of the hex press elicits strong contraction of the subscapularis. This feature might improve  tolerance to exercise or help address subscapularis insufficiency.  Generally, hex pressing tends to be better tolerated than pec flyes and traditional bench press variations by those with banged up shoulders. Again, go see a qualified sports medicine practitioner if you’re dealing with a shoulder injury.