I was thinking along those lines, too. Others say it's just a novelty, but I doubt this ring was designed to be fired at a target, it was designed to be fired into a target, i.e. you lock eyes with your victim, pull him toward you into an embrace, fold down the trigger, run your hand through his hair, press the ring into his temple, and blammo. the absence of a barrel and the extremely low caliber point to this type of usage, anyway.
but, all in all, the novelty value cannot be dismissed, since you might as well stab the motherfucker. I saw a female former secret agent on TV once. she said that when she had to kill someone, she did the above maneuver but at the last moment, she pulled and unfolded a long, thin picnic-type of blade and then right into the neck, which she demonstrated to the interviewer while locking eyes with him. everything the same as the pistol-ring scenario, plus silence; a huge benefit, especially to a field agent.
she was pretty cool.