We don't know if you like this product or not, but according The Firearm Blog, the Pentagon Magazine Coupler and the Opposite Magazine Coupler which is made by the Mako Group/Fab Defense is now shipping. Allows you to have one magazine inserted and 4 more ready to go without going to your mag pouch. Want one for airsoft?

A video from James Madison gives you a more close-up look.

Check the product at the MAKO Group.