I feed Purina Flockraiser 20% (all-flock feed) all the time I can afford it. (And Dumor 17% or higher when I can't). From what I can tell the cost difference is due to protein content and trace nutrients/minerals.
I give them oyster shell and grit in separate containers in the covered run year round. Most hens will eat what they need of the grit and eggshell and the roosters will leave the oyster shell alone.
If you're wanting supplementation, consider rooster booster, also human vitamin B complex (in the water, you can't overdose). Sometimes folks feed human vitamin E or vitamin D for various reasons. Or Calcium citrate with vitamin D for egg shell issues. Nutridrench (molasses based) is also an easy way to supplement trace vitamins/minerals short-term. Probiotics for chickens are also helpful. Electrolytes when it's hot (Hydro-Hen or similar).
If you search on this site, Kiki has a link in her signature to the chicken feed Excel sheet, and that shows the trace nutrients that chickens need in their food and how much of each is in numerous commercial feeds.
16% is really the minimum on protein that commercial chicken houses can use and still get enough eggs from chickens only expected to live for two years. If you want healthier or longer-lived chickens, or better trace nutrients, best to up the protein a bit and pay more attention to trace nutrients/minerals/vitamins is how I understand it.
Good luck!!!