I like Mysterious stranger personally, but it keeps me in V.A.T.S. when he comes up. He'll kill the enemy, then just stand around in his "yellowish aura" with the cowboy music playing, then leave when he feels as though is presence has been acknowledged.
Yeah- I just experienced the same thing........I got Miss Fortune first, and for a laugh (and because my character is very lucky) I got MS too. So, it does wait a while after he shoots the target, to exit vats/that effect. And I thought it was just annoying, until.....
......I fast travelled somewhere I hadnt really been too, and found myself surrounded by deathclaws. So, I go into vats, throw a poisoned knife at one of their legs, and MS shows up. Ok.......so, my character is visible on the right of the screen, MS is standing on the left, facing the camera kinda looking straight ahead. The effect remains, but the game isn't glitching or pausing, nooooo, its carrying on like I'm still in vats, but I'm not doing any actions. The deathclaws are still moving, entering stage (screen) left, passing behind MS like a procession, at least 4 or 5 deathclaws. My character is still squatting there unable to move, and is getting wailed on by these deathclaws, and pushed off the screen (exit stage right). And as you say MS just stands there looking all glowy, and just as I'm about to die off screen he casually turns his head to look in the direction of my character...........lot of help he was.