Commercial layer feeds are made for layers. Hens actively laying eggs need more calcium in their diet, thus the extra calcium layer feed. All flock, or flock raiser feeds don't have all the calcium added. They're meant for layers, chicks, and roosters. But if you have laying hens, they still need extra calcium, so you have to provide it to them in some form. Oyster shell works best in my opinion. And if you offer it in a separate dish, only the chickens who need it will eat it.
