So basically, what you're saying, is you'd rather end up with no air at all, than having to switch regulators?
What I mean is, left tank closed, right tank open. BAM! There goes the hose from the right tank to the manifold, what do you do? You first have to open a tank before you can get air, now if it bursts when you've just breathed out, I'm not sure that's a great idea. Is this really how UTD teaches it, or should you rely on your buddy (which will of course be at the other side of a restriction)? This is a serious question, I don't know the UTD training and probably never will take it, but closing a tank that you're supposed to breathe of doesn't sound too good.