masterfulTypically you only need 3 rockets for a medic bomb, if you are supremely confident in your shots. It just seems a little overconfident to me. Unless you perfectly land your two rockets, you will die without killing someone a good percentage of the time, and even if you do, you can't jump instantly back out afterward.
I just want to make it clear that he isn't using the Black Box because he's cocky and feels he only needs 3 rockets to bomb a Medic. He's doing it because he has more potential to roam and overall can sustain himself much easier.