The magwell hold might be dead on the range, but it's very much alive for anyone in the military or police. You'll notice almost anytime cover is used a person generally goes to a mag well hold. You'll find this especially when someone has to hold the firearm in a ready position for an undetermined period of time yet still be ready to fire. The simple reason is you're stronger and can hold the rifle longer without fatigue. The benefit of the forward hold is you reduce the lever effect which stops over steer for faster target acquisition. The disadvantage is that you've reduced the lever effect so you will fatigue much faster. Unlike the range you may go a very long time having to be ready without actually ever firing a shot.
The rundown exercise shown previously isn't reflective of the reality of running and shooting. In most cases it's to get somewhere while possibly having to shoot suppressive fire. So you'd want to be able to shoot while running as fast as possible. You can't move very fast with the forward grip. You're not going to run right up, sight up from 5 feet and shoot. The only benefit of that exercise is to get your heart pumping the adrenaline going and teach you to then focus while being able to shoot. It's beneficial since that part is more realistic and it's very different from shooting relaxed at a firing line. It's a great exercise but unlikely to ever go that way in real life, unless you screw up.
Don't get me wrong I actually have come around to the forward hold when it's use is appropriate. But that's not all the time and it's benefit is a lot less likely to be used outside a range. I also consider the vertical grip a decent compromise between the two. Especially if you have heavy crud mounted on your rifle. That being said for non combat and police use I still like a clean rifle with no vertical grip, especially if it will be a patrol carbine and the officer has to get out of the car with it ready to go. If something can get hung up it will. From a police perspective I think the forward hold would be beneficial for instances such as rapid response to school shootings once inside the school. You're in a fairly contained area and clearing areas with longer hallways. I could see it being very useful for that and would probably use it in that instance.
Keep in mind that the first tactical principle out of the 7 for Police is:
Cover.
Early use of the magwell hold:
Russian most likely on the Eastern Front with SVT-40
Canadian soldier training with the Armalite AR10.
Benefits of the magwell hold:
1) When
shooting from behind cover you can actually hold your firearm. Note the small walls used in Afghanistan. Or vehicle engine block use for police.
2) When you have optics, bipods etc you can keep your rifle on target easier and for longer with less tiring.
3) When running for it and having to use suppression fire. You're just firing in the general direction while trying to get out of a bad situation. Being able to run full out while making it harder for the other people is the purpose. Especially if you are only one of a bunch of you trying to relocate.
4) When you have a longer barrel such as a 20" like many infantry rifles. Again balance/strength are at play here.
5) For police, you may have to hold that firearm for a long time either covering an area, or on a suspect without ever firing a shot. You're a lot stronger and for longer holding the rifle by the magwell rather than out further.
Here are our guys in Afghanistan showing off the range use and under fire. Good work guys.
http://www.youtube.com/watch?v=DIAfS0HNUVU&feature=related
http://www.youtube.com/watch?v=KQBkgoH7NNU&feature=related
http://www.youtube.com/watch?v=4brC6F91bEY&feature=related
http://www.youtube.com/watch?v=s_WiEvPYBIc&feature=related
Anyways just my thoughts on this. I don't consider myself an expert although I do have some experience off the range.