They're one-of-a-kind. For my world, anyway - I've heard of others out there.

[Mostly in the hands of other Octaviuses. Octavii? Point being, it's weird and he doesn't much want to get into it.]

I'm working in neuroprosthetics here, now. In addition to all the Guild stuff. [He shoots Huvrye a sidelong look, like with his actual eyes.] I can answer any questions you have about them. Easier to do that in person.