I know these extenders are popular with competition shooters, putting them on 30 round AR mags, but this makes the mags quite long, of course. I've always felt a 24 or 25 round magazine would be the ideal length for the AR, so I am interested in trying out a magazine extender on a 20 round gen3 Pmag. This magazine uses the same 15 coil magazine spring as the 30 round magazine.

I know there are aluminum extenders and I think polymer extenders are also available. Which extender would you recommend? Polymer would be fine with me as long as the durability is on par with the polymer used by Magpul. Of course, reliability is paramount.

Has anyone tried a 4 or 5 round extender on a 20 round Pmag?