Most avoid layer feed simply because it is more costly just for added calcium, often lacks in protein, and can cause delayed development, liver failure, etc in non-laying birds. I switched off it and never gone back since. If you have thin shells try letting your birds forage. It fixes everything and creates beautiful bright yolks.
Layer feed is cheaper than grower or all flock in most cases. More protein, more dollars. They don't charge more for calcium. That is what I find amusing when people want to cut costs & are told to by a higher protein feed. Layer is usually not just 16%, especially my locally made feed. It is actually 16.8%, but 16% is used on the label. Chickens actually only need 14-15% to lay. No one is saying to feed layer to young birds. It is just the past few years this board has gone crazy on the higher protein while screaming, I need to save money! Foraging will not help in the winter! I used to free range back from 1993-2004. Not able to anymore since a development went in behind me. Not everyone can free range! I noticed a big difference in 2004 when the feeds started to go vegetarian. No way am I paying more for a 20% feed that is loaded with soy. Once birds are mature, I see no problem feeding layers to them all. Just look at Feather Fixer that is to be given during molt. That has as much calcium in it as layer feed. Chickens are NOT that complicated! Just saying.