Just got 2 in today. My initial impression is positive, but I haven't shot them yet. They lock in nice and solid and drop free easy. Side by side with the PSA mags the quality and finish of the Magpul mags seems much better. I don't think these will take any sanding or other work to get them GTG, unlike so many other Scorpion mags. I have the Avalanche extended mag release and they work fine with it. Being Magpul mags, they feel very solid and I'm confident they'll outlive me. They look good, too.
They are most definitely NOT re-branded PSA mags, BTW, they just look and feel higher quality, and the molding seems superior at a glance. They are notched so that you can tell roughly how many rounds you've got in there. They are also shorter than the PSA mags by about 0.5cm and the retention system cut is slightly different. The hatch pattern also provides a slightly more solid gripping surface than the PSA mags.
If they cycle OK (as I expect with Magpuls) then I will be buying these from now on instead of the factory or PSA mags.