Sex linked coloration at hatch is one thing but that's down, not feathers. When I hear feather sexing I assume the wing feathers as to chicks don't have any. Feather sexing is done at around 3 weeks of age.
It takes a trained professional with perfect eye sight to accurately vent sex. The hatcheries are well over 90% accurate. They use the 90% disclaimer to cover themselves from disgruntled customers.
Feather sexing at hatch makes no sense to me. Chicks don't have feathers.