FWIW: With nothing more than a quick stripping, inspection and cleaning out of the box, my recently purchased compact model has been flawless with 350 rounds of mixed FMJ and hollowpoints fired thus far. It gives up little or nothing in shootability compared to my trusty old Glock 19, while addressing the latter gun's minor shortcomings. In fact, I call it a "better-feeling Glock."
Some notes about the takedown tool: it has a lug on it that fits quite tightly and requires one to rather forcibly push in and twist to seat. After a few hundred withdrawals and insertions I'm not sure how long this will last, but it cannot and has never fallen out while just shooting. It is not just a takedown tool, but actually retains the interchangeable backstraps and is an integral part of the bottom rear of the grip, so it cannot be left out. The little point on the end is designed to flip down a sear deactivation lever, which eliminates the need to pull the trigger to remove the slide for cleaning but does add an extra step to the process. Any similar-shaped tool - or your little fingernail for that matter - can be used for this, or you can just pull the trigger and dispense with this altogether.
IMO your "double-feeding" problems are caused by some fault in the extractor - which is supposed to mechanically/physically pull the case from the chamber - and have nothing to do with "limp-wristing." (BTW, I fired one magazineful out of mine with my left/weak hand and had no malfunctions.) And this business of the takedown tool/backstrap retainer falling out of its own weight suggest some problem with the groove or notch in the frame into which the little lug fits.
Give them another chance, but make it clear - politely - that if not corrected this time they should consider replacing your gun.