Not a big fan of sanding dust or sanding sealer for filling pores of open grain wood. Using sanding dust been around a long time but feel just busy work. Sanding sealer is not pore filler and can soften a final finish.
Apply light coats of whatever top coat of finishing product to fill pores and finish your pen. Better yet thin top coat product with solvent, apply let dry, sand reapply, let dry sand until pores filled and have a level surface, then apply your final finish. Can always use CA as a pore sealer as well!
Shellac, oil blends, poly, and varnish work so well really no need to fill pores. I add lacquer because brushing lacquers mostly self leveling.
Here is an oak pen finished with lacquer, and no sanding dust or sealer!