It depends on the breed. Both my Speckled Sussex had different wing feathering, I knew for sure one was a rooster. Nope, I have 2 pullets. I've been told by Sussex breeders you can't feather sex Sussex. My Easter Eggers & Silver-laced Wyandottes were feather sexed and they are pullets.
When you say you have done it "successfully" - are you able to track how accurate you are can predict the sex? Do you think you get close to 90%? Just wondering, I think it's great that you have had success with the method.
Sure........... I band them after ID'ing them and track them to see if it worked and it does well over 90%. I have done it for some other folks as well and they were very happy with the results and have been doing it as part of their flock management program.