I got 2 of those at the last indy 1500.
There is a dealer there with them for $12 per, no sales tax.
They work great as range mags, no failures of any kind. I still only carry factory glock though...
That was Roger Cope, he is a good guy, here is a link to the $12 mags:
Cope's Distributing
He charges flat rate shipping of $7.95 for most of his stuff except ammo and parts kits.