There is more Tung Oil in the writing on the label than there is in the container. Formby's "Tung Oil" is a basic oil finish that is similar to the Watco Danish Oil that doesn't contain Danish Oil either. These are a ready-to-use oil finish that is a mixture of Soy Bean Oil, sometimes a small amount of Linseed Oil, a drying agent to make the Soy Oil cure, and a lot of thinner.
You can use the Formby's, and it will make a nice looking finish on the pen; but don't expect a hard durable finish. These oils are relatively soft and will wear quickly on a piece of wood that will be handled and exposed to body oils like a pen. A better choice would be a real Tung Oil, or better yet, a product like "Waterlox" that is a real Tung Oil finish with resins added to form a harder more durable surface film.
Oil finishes take a long time to apply. A quicker way to do it is to saturate the wood by keeping it wet, or soaking it in the can, for an hour; wipe off the excess; let it dry for a week; and then buff with the Bealle or similar wheels using both abrasives followed by the wax.