He rabbits on and on to make himself seem smart or important, but for the most part he should be answering questions with single word sentences instead of lecturing to the jury.
By answering in detail, MO gave any jurors who don't know much about guns an understanding of why his answers made sense, and reason to think he knew what he was talking about, not making up answers to help his friend.
I do think MO fumbled badly when Bernie crossed on 'center mass'. Bernie asked a series of questions that conflated 'stop' with 'kill', painting people who carry as bloodthirsty vigilantes out to lure bad guys to their deaths like a Charles Bronson anti-hero. I was, let's say disappointed, when MO answered the first of those questions with, essentially, 'yes, that's right'. By the second such question MO had spotted the trap and was answering correctly. But I think anyone advocating for armed self-defense should be acutely aware of the stop/kill distinction, and react immediately when someone tries to conflate the two.
I think MO also missed the chance to make clear that one reason for shooting center mass is that a miss endangers bystanders. That was particularly important for GZ's situation, at close quarters between two rows of mostly occupied residences.
Still, I give MO a B+. He made a good defense, not only of GZ, but of the practice of concealed carry.