My roosters do quite well on layer feed. I fed all-flock for about six months, then caught Chester (My rooster at the time) picking oyster shell out of the container, and then I compared prices and said, "heck with it."
I wouldn’t want to take the chance of loosing a rooster to kidney disease. Even the hens will have periods of not laying (example: while molting or broody) and they won’t need the higher calcium levels found in layer feed. Just recently there was a member on BYC that lost an expensive & loved Roo due to not knowing that layer feed was not good for him.