As a former Marine, in addition to the difference pointed out by jsteinhardt, the flexed arm hang works your arms only, not your back. Pullups require an overhand grip, whereas the flexed arm hang (and chinup) focus on your biceps.
As a former Marine, in addition to the difference pointed out by jsteinhardt, the flexed arm hang works your arms only, not your back. Pullups require an overhand grip, whereas the flexed arm hang (and chinup) focus on your biceps.