I think that method only works if the chicks are sex linked hybrids, so it probably won't work unless your chicks were specifically breed to have those sex linked feather genes.
There is a Dirty Jobs video you can also find on youtube that shows the vent sexing that is used for a lot of the other breeds when they are sexed at a day old in the hatcheries.
I know it! there is 1 worse then that right next to that video called sexing pullits i think and it was readdy bad they where sexing the and tossing them down a shoot!