It's still a mixto, just like Cuervo Gold, except it's an aged mixto (1 year old), like Sauza's Conmemorativo.
Cuervo is just trying to cash in on the fact that anejo (aged) tequila is catching on, and that many often associate older with better. However, Cuervo Black can't be compared to the 100% de agave anejos out there. The sad thing is that slick marketing is all it will take for people to believe that this is actually a premium product. Marketing is what got Cuervo Gold to its status, although more and more people are taking notice to 100% agave tequila, whether it be blanco, reposado, or anejo, and realizing that Cuervo Gold really is bottom shelf crap. I suspect that many people like me who realize the vast difference between mixto and 100% agave tequila will not even bother trying Black.
My advice would be don't even bother. I'll admitt I haven't tried it, but from past experiences with mixtos of any kind, they simply cannot come close to 100% agave tequila, which is the only real kind of tequila if you ask me.
On a side no, Cuervo does make a 100% agave reposado called Tradicional. It's not great, but it's drinkable. I would definitely consider it a mixing tequila though. The funny thing is most people who drink Cuervo Gold don't know Tradicional exists. Why? Because if Cuervo were to market Tradicional as a better tequila because it's 100% agave, wouldn't that imply that the Gold is inferior? And lord knows Cuervo spent too much on billboards, commercials, and magazine ads trying to build the image of Cuervo Gold to let people begin to question it now. That's my guess anyway.