I can verify that most of the negative comments about A-MERC brass from my past experience (mis-aligned flash hole, poor case dimensions, poor case finish, etc.).
While going through the range brass from this past weekend's shooting, I found enough "new looking" A-MERC brass in the mix to think that someone shot a new box of them. I carefully inspected the spent casings and all the flash holes looked good. I am planning to clean these separately and see if the deprime/sizing goes ok and reinspect them. Perhaps they improved their production/quality control process? I doubt it, but will give them my benefit of doubt by "stress testing" through repeated reloading. Of course, older A-MERC brass you may pick up in the range brass mix may not necessarily be new, so I would be cautious with them (I normally segregate them for scrap).
I am planning to "stress test" these cases with various powders and charges that are near max. I will also use several new Winchester/Remington/Federal/Speer/PMC, etc. cases to use as reference and see which brand cases fail first or show signs of stress.
I got cases that have over 50-100+ reloads so this may take a while.