I use this kind off duty. BLACKHAWK! Double Stack Mag Case Matte Finish - BLACKHAWK!
It holds glock 40cal/9mm mags with just the right amount of tension. If you are running, fighting, ect. the mag will not come out but when you need it out for a reload it comes out smoothly. Keep in mind this is on a 511 trainer belt. Like a holster you need a good belt to really take advantage of this mag holder.
I use the BlackHawk like JBGlock but I use the Double Mag Double Stack. I have also used leather and do love them too. Are you looking for Leather or Polymer? BlackHawk makes good products, they even have leather pouches. DeSantis and Safari are also very good leather makers. I look for pouches that have tension screws so I can adjust them to fit the mags I'm carrying