Gents,
I have been using one of these for my AR (check the classifieds section for the AR in question and the worlds longest for sale thread!!).
This is the FASTEST way for me to get a reload in the AR15, I have tried some of the open top mag pouches and they are quick, this allows me 3 reloads that are lightning fast.
Shown mounted to my Eagle RRV/Rhodesian Recon Vest (an excellent item too!) Mine is in OD Green but skins are available in all the usual colors to cover the unit with.

Go to the web site, check out the videos of this in action.
http://www.stractech.com/NOTE: I know the owner of the company, but I never recommend anything that I would not use myself, in this case, the RRV/STRAC combo rides with me on patrol then in my truck. Awesome gear.
Andy
(if you call/email them, tell them " Andy that crazy guy sent me...." !)