For me personally, and the way I shoot, I like the AFG. If you shoot with a thumb over grip, it's definitely worth trying out an AFG. I haven't tried some of the other options that are out there, so I can't say that it's the best, but it's good. At some point, I'm gonna pick up either a Spike's SAR or a DD Lite Rail, when that time comes, I'm gonna try out some of the hand stops that are out there, simply because they're smaller, lighter and more streamlined. Something like this:
LaRue Tactical HandStop and IndexClip Combo, 74 Total Piece Set | LaRue Tactical
But with the handguard that's currently on my rifle, the AFG is the only viable option. Some people who shoot thumb over run their rifles with no sort of grip or hand break/stop on their rifles, but I don't have the kind of muscle memory for that yet, so I like to have something to use as a, for lack of a better word, "place marker" on my handguard. That way I know my hand is on the exact same spot on the rifle every time.
In contrast to that, some people like to run vert grips, or do like you have done, and just grip the magwell, and that's cool. I've always said do what works best for you. Neither of these methods work for me, and I'll tell you why, then you can make your own decision.
The magwell grip is really popular with a lot of military guys I know. Using that grip style, you can probably swing the rifle a little faster, but in my experience I have way less control. I get a lot of over swing and sway.
For example, take a broomstick and grab it in the middle with both hands, with about 5 inches in between your hands, then have someone grab the broomstick and try to move it around. Then do the same thing, but leave about 18-20 inches in between, and have them do the same thing.
I bet they were able to move it a lot more when your hands were close together. The same applies to the rifle. When you're swinging it, and you stop swinging, the momentum of the rifle can cause it to kind of shift in your grip, what I'm calling over swing. Plus with my hand so close together, I'm not able to point shoot very well. (More on this in a minute).
Vert grips look cool, but for me, that's about all they do. For me, they are uncomfortable and unwieldy. After shooting for a while, it starts to make my wrist cramp up. However, my biggest problem for me when using a vert grip, is it puts both of your hands below the bulk of the weight on the rifle, causing it to sway and can't bad when I'm swinging it, and it just feels like I have less control.
I like the thumb over grip for 2 main reasons. #1 It's very comfortable for me. #2 It's super stable.
Using the thumb over, I can shoot for hours and not have my wrist cramp up.
As far as stability goes, it can't be beaten in my opinion. Your hand is way out far on the barrel, so it really helps with reducing muzzle rise, and keeps the rifle from shifting in your grip when swinging, reducing over swing. It gets your hand up around and over where the bulk of the rifle weight is, keeping it from swaying in your grip. Lastly, since I've got my hands stretched out, with my support pointing straight at the target, I find point shooting much easier and much more accurate.
As always, experiment and draw your own conclusions. There is no right or wrong way to grip a rifle, there is only the way that works best for you.