This is what i read:
http://www.mangatoshokan.com/read/bleach/1/346/20

The wiki page just says ‘This Cero presumably can only be used while he is in HIS release state’.

I suppose different groups provide us with different translations.
Sleepyfans translated: ‘This is an Espada’s fully powered Black Cero’. Note he didnt say ‘my fully powered cero’. Maximum7 translated: ‘This is something only a released Espada can do.’

So both groups translations indicate that this isnt a unique move. It just appears so, since no one else has used it. Same thing with the Gran Rey Cero that Grimmjow shot off just to force Ichigo to draw his mask.

They probably havent been used thus far by anyone else because; 1.) the characters in question are too proud/full(/even bored perhaps) of themselfs they dont bother to use them. Or 2.) to make the Main character fights still stand out above the rest. To make Ichigo look like he keeps on growing above everyone else in strength. Some ‘killer’ move will just enhance that fact.

Two guns vs Two captains. I hope Tite keeps the focus on this fight before something else with go on. I hope he goes back to Hueco after this, since the Shinigami almost control Las Noches with the exeption of Yammy. I wonder is Las Noches still stands after that fight. The roof got a beating already.

and i didn’t forget about the cero obscuras pretend3r, i just think that it was something unique to ulquiorra. i think that since he didn’t use a gran-rey cero, it must have been his equivalent to it.

speaking of the gran rey cero, why have we only seen grimmjow use it so far. if it is so powerful, you’d think some the other espada would have tried using it before being defeated. i don’t think it was unique to grimmjow because i think he mentioned all espada being able to do it. i’m just puzzled as to why others havn’t. since stark seems to be the cero master of the espada, i think he will probably use it. and perhaps reveal other new cero types.

This fight is shaping up to be awsome. Kyoraku and Ukitake. Kyoraku isnt wasting time with Stark, tho he doesnt seem very impressed. For some reason Kyoraku still seems to be acting somewhat playfull(if im even allowed to use that word) until Stark major attack.

Assuming stark’s guns fire cero’s there is still the Cero Obscuras(dont tell me you forgot that one…). And Ukitake… well… damn. If he can blast away Stark’s Cero so easily, his Bankai is gonna be very impressive. Lets just hope his health stays in good order. If not, well, there is still Kyoraku and his Bankai..

Me happy.

I’ll agree, even though stark’s ressurection isn’t some god-like being, its still bad fucking ass. the gun is cool, and about the other thing it fires, i think whatever else it is, it comes out of his other gun. i think the right gun has an arsenal of cero ammo, and its strongest bullet is probably its equivalent to the gran-rey cero. the other gun’s ammo is a mystery to me, but whatever it is, it is definitely stark’s trump card.

as cool as his release is, so far it hasn’t quite lived up to my expectations. i mean yes it is cool, but i guess i just expected the primera to be godly strong, like to the point where he wouldn’t struggle at all with these two… oh well im sure he still has much more to show, maybe even another release… please?

shunsui is strong, but like i said before, my money is on ukitake. i think his bankai will be the most impressive of them all.