This thumb over thumb grip is just the latest fad grip technique. To me it doesn't make any sense to put your weak hand in position to interfere with the slide, slide stop, safety, mag release, etc. when you're shooting in a stress situation. Contrary to what the guy said, you actually have less leverage against recoil / muzzle flip than if the weak hand was placed lower on the grip, where it would also insure that the mag stays in the gun.
** Link removed per remote admin, 5/8/2015 wlc
I'll listen to Travis Healy, who actually has experience in combat, plus gives solid biomechanical reasons why the "latest fad" grip is so effective; than listen to you (what are your qualifications?) who uses some Big Army manual as justification for an ineffective grip that has been abandoned by virtually every action pistol competitor on the planet.
Weak hand lower on the gun gives more control over muzzle rise? LOL
Cup and Saucer and Weaver grips? LOLOLOL
You also might want to tell Frank Proctor, Ben Stoeger, Adam Tyc, Angus Hobdell, and a host of other USPSA, IPSC, and IDPA champions that they are doing it wrong.
http://youtu.be/tMzQIHN-LiI