Ketubjörg is not a polished roadside waterfall. It is a wind-exposed sea-cliff stop on the Skagi Peninsula, where water drops through dark coastal rock toward Skagafjörður and the ocean below.
The best reason to go is the combination: cliff edge, surf, bird movement, and the odd drama of a waterfall that does not continue into a river valley. That makes it more memorable than many small detours, but only when the route has enough slack.
Leave it out if your North Iceland day still needs easier anchors such as Akureyri, Goðafoss, or Mývatn. Ketubjörg belongs in a slower coastal plan, not in a rushed checklist.