There are a lot of ways to carry spare magazine's for your AR. Some folks have chest rigs and belts and outfits that would intimidate a Navy SEAL or even the most over-equipped mall-ninja. There's nothing wrong with getting good equipment and practical ways to carry it, but sometimes more is actually less.
The gals and I often keep a rifle handy at night in addition to our other self and home defense firearms. When something goes bump in the night or the wiley coyote ventures too close to the house or barn... some folks gear-up, but we usually just grab the rifle. Having an extra mag for the rifle is always a good idea. The Magpul MagLink Magazine Couple allows you to do this by keeping the spare mag right on the rifle.
The coupler is made to work with both Gen2 and Gen3 PMAG magazines. It locks them securely together and you have some positioning options with the coupler and the magazines. Reloads are quick to index with two PMAGs perfectly spaced apart for fast insertion in the mag-well.
Yeah... two fully-loaded mags add weight to your gun, but when you grab your rifle in the middle of the night, you don't have to slow your self down grabbing and extra mag and stuffing it in your pocket or take the time to "kit-up" with a full chest rig. Not this set-up will limit you to about sixty rounds, but at least you're not bumping around in the dark looking for your extra mag or chest rig.
I'm not saying that other "kits", chest-rigs, and gear don't have their place, but this is a good way to Keep It Simple, Stupid with rifle... So if you want to keep it simple and straight forward, go with the Magpul MagLink Magazine Coupler: More KISS