I stopped in at Vitamin Cottage (they sell organic produce and bulk foods in addition to vitamins) to see if they had rennet (they didn't) and picked up some eggs while I was there. Not these eggs. These eggs I just picked up a picture of.
I checked around online, and found that fertile eggs don't have any added nutritional benefits. So why buy them?
There should not be any developed embryos in them if they were collected promptly and stored cold. If you were to find one that had reached the balut stage, you would be right to complain (unless you like balut).
On a backyard chicken forum, I found that you can incubate these eggs if you get a batch that is not too far out from being laid and has not been kept below 50 degrees. But you'd get a much better success rate with eggs from a local farmer.
"The hens are ISA Browns or Bovans, and the roosters are 95 percent Hyline w-36 Whites." Whatever that means. ( I should clarify: that info came from the chicken forum, not the carton. These eggs are meant to be eaten, not incubated.)
These are Southern California chicken eggs, from Chino Valley Ranchers in Arcadia.
Again, why would one buy fertile eggs?