I've had this software for a while, but never could get it to run well. I know it's supposed to still be in beta, but...
Black Ink just doesn't work well on a Cintiq Companion. It has very slow brush tracking and weird jumps in the line. The only solution is to disable precise stylus tracking, which means less smooth lines. It does work a lot better (and way faster) with a capacitive pen, if you don't mind loosing pressure sensitivity, that is. Also, touch support is poor, with very slow pinch to zoom and no panning. Take a look at the latest update for Manga Studio 5EX if you want an example of how pen and touch are supposed to work together.
On a gaming PC with a Cintiq the tracking problems and wobly lines are also present, but at least the performance problems are gone.
At this point I have lost interest in digging deeper onto Black Inks features. There are too many drawing tools out there that do work well, even on a tablet. A shame, really. I do still like the concept. Perhaps I'll take another look once Bleank finishes the software.
Generally avoid if you plan on using Black Ink on a tablet/slate PC. It needs a beefy GPU and is too slow on an Intel HD 4000 (confirmed by the developer). Also be prepared for possible problems drawing on a Wacom Cintiq. Try the demo before buying!