This exercise is a great transition to develop strength for the one armed chin up because in the transition move you are holding yourself up with one arm. (ashotofadrenaline.net)
I'm going to get a solid Batman push - up one of these days, but I suspect I'll get a dead - hang one - arm chin first. (beastskills.com)
One - arm chins seem not to be as rare, and I've seen them done for reps with perfect technique. (beastskills.com)