Sure, training matters. Alot. In the interest of friendly discussion, here's my brain dump:
Why is it, do you think, that no one teaches your grip? There's no doubt you can train yourself to be good at this technique, but that doesn't eliminate several unavoidable problems inherent in this technique. I just think it's unecessarily complex, limited in utility, potentially unsafe, and a waste of very limited training time. YMMV.
One is that your two hands have to be in contact, and in motion relative to each other, to activate the light. It's impossible to turn the light on/off if you have to separate the hands, like when opening a door, if you get bumped or jarred, or change magazines. Any shift in grip or position of either hand removes your ability to control that light until you reacquire that precise grip.
And, in sticking your thumb out there to push on the button, you potentially weaken your strong hand grip on the weapon. If your chosen method of turning the light on/off is to pull the weak hand back against the thumb, then that hand-dance is likely to disrupt a solid two-handed hold as well, isosceles, weaver, or whatever.
While pushing with one hand and also pulling with the other isn't by itself a difficult task, it's really, really important that you don't get those two things mixed up when one of those motions presses a trigger.
FWIW, all the holds you list use a single hand (the off hand) to activate the light. And it shouldn't surprise you that it's the same hand holding the light. Chapman/Ayoob are for side-mount switched lights, like the Kel-tec/maglights. The Surefire ("cigar") hold is for a tail-switch light with a combat ring. All are designed to allow the user to activate the light without shifting your grip. Harries has been used for both.
Yours requires two hands to work, either pushing forward with the strong hand thumb, or pulling back on the light with the weak hand. Your technique only works if you maintain that specific grip. If you have to separate your hands and need to use the light, you now have to readjust your grip to turn it on/off. By necessity, you have to shift your grip to weak hand thumb on the switch, and use one of the above shooting positions, or a neck hold or mod-FBI, or something. Why bother?
One other thought- all the traditional techniques allow the user to acquire their light ready to activate. Holster, holder, or ring, grab it and it's ready to use by itself, or brought together with a weapon. To search without pointing your gun at everything is really the only reason NOT to have a WML. I have no idea how you could carry that light to get it into your hand in that position without a bit too much spinning, turning, flipping or whatever for me. Plus, you risk dropping that little light when flipping it around to turn it on one-handed.
Does anyone teach this method?