They have one advantage that is worth mentioning but of lesser importance to me... the inks are very forgiving on cheaper paper. Bleed-through of course, but hardly any feathering and normal drying times. On the super smooth Original Crown Mill Vellum, the ink almost floats.
This ink is no exception. I didn't like it much in my Parker Duofold (medium nib). In a TWSBI Eco (Fine nib) it is a decent black. Darker than I expected, little or no shading, some bleed-through even on Rhodia. Drying times on (smooth) paper are very high, more than a minute.
When comparing the ink to other blacks I was surprised to see it turned out darker (with glass pen) than Aurora Black, allegedly the darkest black available on the market.
N.B. paper used is original crown mill vellum paper