Quick update for anyone interested:
Just got back from the range where my Scorpion flawlessly cycled 355 rounds using my factory mags (200 Speer Lawman TMJ (flat nose), 100 American Eagle (ball ammo), 40 hollow points, and 15 underwood extreme defenders (plus sign nose shape)). The good news is I didn't get a lemon Scorpion, the bad news is this just became a review of the Manticore magazines.
I know a lot of people have used these magazines without issue, and my impression is Manticore is a good company. If they came out with an updated version of these that reliably addressed the feeding and failure to lock back issues, I would definitely be open to giving them a second try. For now though, I'll be one vote against ordering them for yourself (though there will undoubtedly be dozens of happy users here that will tell you otherwise).
Thanks again for all the comments, I appreciate your input.