"Either use the laser and ignore the irons, or shut off the laser and use the irons".
But the fundamentals of instinctive, rapid, defensive handgunning are the same for all shots. You really CAN'T train two completely different rapid emergency responses to the same problem. Defensive training and competition practice have trended toward isolating the quickest and most effective human responses to needing to engage a hostile threat with a handgun, and that's summed up best in the 4-count drawstroke and presentation. There really isn't another pseudo-presentation that works nearly so well, which is why no trainers are teaching the old FBI-crouch, or the "speed rock" or any other variations any more.
Introducing another, parallel, path of response just to be able to close off one sighting system choice in favor of another involves far too complicated response, and even more importantly, adds an entire "OODA" loop within your "OODA" loop. That's going to introduce quite possibly fatal lag.
The only way to be close to on-target with your laser from the draw is to bring it up into your workspace and push it out in the normal presentation, using your body to index the muzzle direction and "dressing" the sight picture as you push out to the shot.
(The closer the threat, the more urgently you need to shoot quickly, and the less precise your aim needs to be, so as the target gets closer, you can shoot from a rougher and rougher index, all the way back to "position 2" of the draw, i.e.: the "retention" position.)
If you are trying to adopt an alternative sighting "track" the decision path would have to work something like this:
1) Observe the threat
2) Orient to meet the threat
3) Observe the conditions.
4) Decide the conditions require the alternate sighting system (laser).
5) Draw the weapon in your "alternate" style, to keep the sights out of your view. This loses your body index, and/or disconnects your normal sight picture "dressing" procedure from your regular eye-hand coordination. (In other words, you're now holding the pistol off-line somewhere -- wide or low probably -- and now attempting to put the dot on the target from an unnatural angle outside of your cone of vision.)
6) Orient the sighting system -- now more difficult because you don't have the benefit of a standard push-out presentation along your line of sight.
7) Act (Shoot).
This CAN work, of course, but only if you're given the great benefit of several precious seconds to work all these things out. If you envision the scenario you're facing to give you plenty of time to decide and act and the chance to present the gun and aim it carefully (maybe the threat doesn't see you yet? Maybe he's just very generous...) then surely you could get the dot on him, move it to some vital spot, and shoot.
But if you're thinking more in terms of
fighting with a handgun, then you cannot possibly build in processes that give you this kind of time benefit and "best case scenario" planning.
The less you have to decide, the more likely you are to be able to do what you have to do in the time you have to work with. Anything that introduces "options," decisions, evaluations, and complexity in using your tools is a bad, bad thing.
