Banderas didn't have to actually hit anything - the script writer was on his side.
Seriously, like a lot of other things, I have tried it. I could do quite well point shooting with two guns, but not firing at the same time. Two problems. First, it is easy to fire two guns at the same time, but very hard to train to fire rapidly alternating shots. And it is even more difficult to alternate rapid shots and keep concentration on both guns. Worse than watching a very fast tennis match; it takes too long to shift attention and aim from one gun to the other.
If it is just a matter of "laying smoke", then firing, say, two DA revolvers at the same time is pretty easy. But while the two hands can easily mirror each other, alternating is hard.
FWIW, I was playing games in a safe area. I never even thought of carrying two guns (and in fact, never even carried a backup gun).
Jim