I fished with a guy on a freshwater river once who used two of them on the back of a skiff. Worked well enough in his situation.
He later moved them up front when we went Crappie fishing.
Just remembering what they looked like (Ya' know, that "pitchfork" shape, or to truly use nautical terms "trident" shaped!) I'm not so convinced they would work well with planer boards. I've never seen ANYONE run planers with them.