There is no difference in taste or nutrition between non-fertile and fertile eggs. When you crack 'em open, the white spot that is normally on the yolk will look just like a little bulls-eyes, with a dot in the center, if the egg is fertile.
The ONLY time you would find an embryo developing in an egg is if it has been incubated for a couple of weeks, either in an incubator or by a broody hen who has sat on the eggs incubating them 24/7 for a couple of weeks. There is NO development until an egg is incubated, and then it takes around 5 days before you see anything at all like veins starting.
Most chickens lay their eggs and leave the nest. Eggs require a broody hen to stay on 'em to start developing. If you have chickens, and a rooster with the hens, just gather the eggs daily.