Sam,
I used to buy from the Petco in Denton and I bought them individually. They had them in bags, in a bucket, in their freezer. The only thing I noticed was, when I switched from Petco to Big Cheese, the mice from Big Cheese looked more "pink" when thawed and the Petco mice looked more "red." I'm not really sure what this means, but I think beef turns a deeper red when it is aged, so I assume the mice I bought from Petco were dead longer before they were frozen than the ones from Big Cheese....but just a guess....my snakes ate them. And, if that is the case, then I guess it would be like feeding your family meat that had been in the fridge a while....not quite sure what you might get along with the meat.
Hope this helps.
Cindy