I offer mine both. I keep a little chicken/sunflower coffee cup on the counter. When I use the egg, I rinse out the shell and let it dry for a day. Then I crush it up and put it in the cup. When it's full, it's off to the coop I go. I can tell you that I purchased a very small bag of oyster shell when the girls were brought home last year. I still have 3/4 of a bag. I have refilled the little dog bowl one time in a year. Everytime I take the eggshells out there and spread them around, they are gone within 24 hours. They don't get all their shells back, my tomatoes get some, and I give eggs away. I do have one person (my stepson) who knows that I give the shells back to the girls, and he has been keeping them for me too.