OEM Glock mags are built like a tank. If you've ever removed the polymer from the steel body, it's basically two mags in one. The steel insert is a work of sheet metal and welding art.
Keep in mind that the original NFML mags were specified and designed to NOT drop free, per the Austrian military requirements. They were also likely designed to keep Schütze Schmidt (the Austrian equivalent of our Private Snuffy) from taking them apart easily. (After they added the lock-plate)
The biggest problem and complaint I've seen with Glock mags over the years (been a Glock Armorer since 1999) is that it's difficult to disassemble the mag for cleaning or service. I've seen more mags buggered up from folks who didn't have "the touch" required to properly disassemble them, than any other malfunction. The shorter the mag-the harder it is too, giving rise to all kinds of aftermarket gadgets to assist with this.
Magpul went the right direction making a durable, lower-cost alternative to OEM while making it easy to disassemble. I see this as the first pebble thrown in the pond of handgun mags. I can't wait to see what the ripple effect will produce in terms of other pistols/calibers/accessories...