Feather Sexing Day Old Chicks: Does it work?!

In this video I show you how to examine day-old chick feathers, how a boy chick's feathers should look different from a girl chick's feathers, and in a few months I'll know if the results match the final hen or rooster!
Most people hatching chicken eggs are hoping for hens, and there are a lot of ways people have tried to sex chicks before they crow or lay. Most don't work - hat trick, anyone? Vent sexing is the best early way to tell, but if you don't do it well you can injure your chick.
The science of feather sexing is basically that, because feathering speed is sex linked, if you have a mom and a dad with different genes for feathering speed, the female chicks will express both at birth and the males will express only one. For it to work properly, you need to know that the parents are a breed that expresses these genes, and which gene each parent carries. I don't know any of that for these chicks.
But, I'm hoping that female chicks are more likely to have different length feathers at birth and males are more likely to have uniform growth, so even if it's not perfect this may give me a better idea of which chicks I should get attached to, and which will have to be given away. Or maybe I just have a very poor grasp of mendelian genetics.