Before you use BLO to pop the grain in combination with a shellac / wax finish on a really nice pen, try it on a scrap piece of wood. You might find you end up with a sticky mess over time (especially if the pen spends any time in the sun) as the shellac / wax wear away with use. Even if you use just the tiniest amount.
A CA or polyurethane finish over BLO can look stunning. These film finishes seal in the BLO.
With a shellac / wax finish, you might find tung oil or treated walnut oil as a better choice.
Wipe some BLO on a piece of glass / metal. Let it sit there for a couple of months. After a couple of months, you'll likely find that it is at best a soft gel. I keep a vat of BLO in my shop to soak thin walled woodturnings to get a translucent effect to the wood. My 8 year old vat of BLO just gelled this year and needed to be replaced. It takes a long time to cure, and it never really gets hard (unless mixed with something else, like poly). I've seen woodturnings on display at craft shows exposed to the sun. The ones heavily treated with BLO and not sealed with a film finish will leave oil stains from the BLO weeping out.
All just my opinion based on my experience. Others with different experiences may have very different opinions.
Ed