I filled one of the Tria brush markers with India ink today. I had to wet the brush to get the ink flowing, and that is why some of the lines are a little pale here.
The fibers of the brush are not very elastic or springy, which means it's hard to do dynamic and energetic strokes. But the line variation is good, and the ink runs okay - not fast enough to keep up with a broad, sweeping stroke, but then that adds a lot of texture with the paper peeping through.
I definitely look forward to experimenting more with this, and hope the brush doesn't clog up with dry ink!