slugthrower,
I don't just practice this with aiming but also in point shooting as well almost from the hip. Nevertheless, it does leave my left arm occupied while it could be fending off as you said.
Some say "SD isn't going to be a fast draw thing" but I disagree with that because the element of surprise is not going to be on your side half the time (this is why I am not a big fan of ankle holsters
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Such is the case, for me, it makes the semi auto too complicated a weapon which is why I stick to carrying a revolver 75% of the time. However, I do carry a semi auto sometimes just to stay familiar and comfortable with them.
I am not as big a fan of carrying with one in the chamber as I used to be. Old school advise has taught me otherwise. I've learned to heed it.