Practice is key to anything, of course. Repetition is king for developing speed. These guys that I'm talking about are reputed to spend long periods of time drilling in nothing but drawing and firing singles, double-taps and controlled pairs from that carry method. When I say long periods of time, I'm talking the kind of reps that ingrain something in your muscle memory (like 10,000+). Since I
can't cite my source, I won't say what the time from the beginning of the draw stroke to completion of two shots is because no one would believe it (I didn't) but most people would say that it's impossible. It IS impossible as anything but something so ingrained as to be instinctive. It's like a flinch rather than a reasoned response.
To head off anything about the
reps making it fast and that the technique itself isn't fast, I've done nowhere NEAR 10,000 reps and I can do it faster than any drawstroke from an OWB holster with NO covering garment even now and I haven't practiced much in terms of handgun skills for nearly a year.
Anyway, it's NOT a good general-purpose carry technique at all. Roadkill Coyote is correct, in general, when he says that it's a sign of complacency because that's exactly what it IS when done by most folks.
It is NOT, however, automatically a sign of a poor gun handler or of someone who doesn't know anything about firearms. In a small percentage of cases, it may be the EXTREME opposite.
I would never advocate this carry method for those who carry for solely for a defensive purpose but it IS a valid, safe and effective carry technique.