Greetings and Salutations to one and all.
'Rap, Pard the other Pards/Pardettes have told you just about right. It is a valid technique, but probably an advanced one. If one has practiced, and is comfortable with the technique it can be deadly fast on big close dump targets. However, it has more risk of a miss, or other fumble.
I am of the opinion that it can be one more tool in your kit.You may never use it as a shooting technique, but it is good to know how. Yup if you shoot gunfighter you will never use it in a match.
Elmer Kieth discribes a different hold, and then tells about a real gunfighter he knew in his youth who won a gunfight with it. I think it is in "Hell I Was There." But it might be "Six Guns" It is a "Period Correct" way to do it, the old timers did it, I just don't know if it was the winners.
Just my two bits in the kitty.
Regards, Beaumont