Well, that thread was certainly a can of worms!
FWIW, my girls get the mix, a 'complete' poultry mix (seed mix, I think in the US you call it scratch?), free ranging, some scraps, and I have introduced layer pellets as well. Also free choice oyster shell. I think I am backing it all ways!
It does vary by season, I have to limit their free ranging in the winter when more foxes are about. My eldest is 9yo. I live in farmland, but small acreage, in Australia. Soil is fairly poor.
They also manage to catch the odd mouse (and manage to swallow them), but they love baby mice (easy to swallow). I call them 'moysters' because the girls swallow them down like that.
I am not so sure 'they know what is good for them'. Given, I have to cover my glass if I sit out with them with a glass of wine or beer.