I have three Ayam Cemani birds that were hatched this spring by a broody Bielefelder. She has hatched me a couple of dozen chicks over the last three years, and these are the only ones that have ever turned out to be so nervous, so I have to assume that it's the breed, and not the way they were raised.
However they are beautiful birds, with a calm (if very nervous) nature. I have two pullets and a rooster, who started to crow at 7 weeks old! He crowed half a dozen times over a couple of weeks, then stopped, and didn't start again until he was over 4 months old. He has just started mounting the hens, and he is very gentle with them - not agressive in any way. He is braver than his sisters, and will happily come and eat out of my hand, although I can only touch him when he is on the roost at night. His two sisters are very flighty - scared of their own shadows, and need a lot of persuading to even eat out of my hand.
It takes a little effort to get the perfect Ayam Cemani rooster, but when you see one of these incredible birds crowing from his favorite roosting spot, it is all worth it. An absolutely stunning bird.