My brother just got back from Hawaii, and received a board from Robin Mair, with Robin's Hanalei Quads, with the Hammer Fins in the rear.
Initial feedback - My brother was really surprised how well they went.
You can stop reading now, if you're not into quads, or not into anything that looks experimental, or not mainstream!
(PS - this is not an infomercial, and I have no financial association with Robin Mair, Mair Surfboards, Hanalei Fins, or Pro Box)
OK, we might have lost a few people by now !
My brother's board has Version 2 of the Hammer Fin, and the Hammer Head Piece is angled up at about 25 degrees. The Hammer Head above is basically angled at Zero degrees. Plus the final tip is pointy. Sorry, no actual pics, I thought it was the same fins from the website, but his board certainly has a new version of the fin.... (See dodge photo).
I have not riden them yet, but from his first comments, I'm keen to drop them into the McTavish Rincon '68 (a mid length man's board), to see how they go on the points down here. (There are more pics of that board on my profile.)
PS - Big thanks to my brother for picking me up after a solo Down Wind run this arvo! That's what brother are for !! I still slung him a 6 pack of Boags Draught though !