That's right... I've heard a lot of talk of feather sexing, had a guy tell me just the other night he wanted to come over and get some but he wanted to feather sex them. Told him knock yourself out...but it doesnt work.I'm no Sumatra expert but I do know that you can only feather sex some breeds of chickens, not just any breed. Many (maybe even most ?) have to be vent sexed which is difficult to do accurately, according to Mike Rowe, anyway. Lol
I just wait for feathers to develop. If you start to see shiny, thin, pointy too feathers on the saddle and hackles, it's a too.
The breeds for the most part that you can do that on are production style birds which threw years of genetic engineering now have that built into them.
If it were that easy and reliable, hatcheries wouldnt pay sexers a ton of money to vent sex all their sexed offspring, they'd just look at the wing feathers, any minimum wade person could do that....
I deal pretty much solely in bantams and for a fact it doesnt work on them. Tested in a lo of birds in years past just to see if there was anything to it.
Like you said, without a magnifying glass and knowledge of what you are looking for, time is the only way to sex these. Shinny feathers, and pointed hackle and saddles is the best way to tell for sure