They do look more rounded to me from that pic and the comb is still on the 'concave' side, so may just be moving early... Some will always keep you guessing, so keep an eye out.There may be a bit more sheen (that or I'm convincing myself there is lol). The tail is worrying me but a few look like they were nipped at so that may be giving it more of a sickle look. Hopefully anyway.
Here's comparison for comb/wattles with the possible roo and a pullet. I noticed the comb growth in the past 2 weeks or so and it hasn't gotten much larger since. I don't see much about this breed either though
And a look at feathers.
I know cemani are quite a shiny bird in general; all my boys with some black feathering(the 6 or so I've hatched) seemed to get it in their first feathering and I would expect such a shiny breed to show pretty much as soon as their wings are mostly in and they've started getting some back feathers.
My 4 1/2 week old black orpington boy has a sheen though he's still pretty bare in the feather department. His sister, no sheen to speak of and pretty much fully feathered.
When I did a SLW hatch, all the boys had a sheen in their black lacing from around 5 weeks that the girls never got.