Can't comment on chicken breasts as we haven't bought them from Costco, but did get some Tenderloin from Costco and it was not great..and we paid $15.99/lb when I could have bought a whole tenderloin from my fancy specialty butcher for $12.99/lb - ultimately it would have been close in cost / lb even after trimming and butchering..
I haven't yet found any proteins at Costco that are "worth it" (well, maybe their Pork Shoulder or MAYBE baby back ribs) compared to other sources, FWIW..obviously pays to shop around and compare not only price but quality..the net differences in cost in my experience are pretty minimal, but the quality differences are very noticeable. And when DW and I were eating the Costco tenderloin last night and commenting on how "meh" it was, I quickly forgot about the few pennies per lb I MIGHT have saved over other sources..I'd gladly have paid another $1 or $2 per lb for better filet..
I couldn't disagree with this more. Costco had by far the highest quality of meat as compared to any conventional grocery stores. I dealt with them fow many years and I know of their standards. Now in most parts of the U.S. people don't have access to a local butcher so this is the best alternative.
We buy the breasts and tenderloins all the time and put in the freezer for later use. Due to the thickness of the breasts I have begun pounding them down for uniform thickness and don't overcook.