I emailed the guy who posted the video on YouTube and he said that it was designed for either keeping your primary mag on the weapon at home, or for storing your spare on your weapon when in storage / nightstand. He said his uncle (a product tester for some distributor) was testing the weapon at the range to see if it or the mag would fly off the gun.
I think it would be fine for keeping a spare mag handy for if you ever needed it in the middle of the night, or if you did not want to keep your gun loaded while it's in your nightstand (kids), but as for carrying it mounted on your weapon at all times seems a little silly.