the problem is that India ink will really gum up the nib and ink delivery system. Once set up, India ink is like cement.Youd have to keep the nib at least moist so the ink doesnt set up but you still will have to spray the nib with plain water to force out any of the ink particles that have begun to set-up
I usually use dippy pens and crow-quills in the studio but doing field sketching, its too much of a hassle. Ive used these disposal pens but they arent color fast, if you do a water color wash over them, the ink will bleed. I often use a light table and trace my field sketches but tht will look stiff almost like its a printer copy.