Folks seem to be down on the carbon filaments here.
The idea that the carbon-filled filaments are stronger is bunk, yes, but I’ve found my prints are more often stiffness-limited than they are strength-limited, and carbon-filled PLA is very stiff. I believe it’s stiffer than polycarbonate, and very easy to print on a printer that can handle it.
Also, the very-black matte finish should not be overlooked. I print a lot of opto-mechanical components and carbon PLA is the clear choice, both for the stiffness to weight ratio and for the optical qualities. In cases where impact resistance or the absolute best tensile strength isn’t important, it’s wonderful stuff.
Incidentally, I just discovered today that the hobbed wheel on the TAZ doesn’t seem up to the task of reliably feeding carbon PLA, which is aside from the issue of the nozzle material.