There is one exception, the soft top.
Those floppy boards are best with 3 (or more) short stubby fins that survive running into the ground.
Who doesn't like riding soft tops all the way to the beach?
finFoil: free fin designing software
...hello; so I watched 2 videos, one with I think Purchase riding an small shape in a head/over head long tricky left walls. Steeped but not toobs either. The other, another Aussie surfer riding bigger long point right walls with strong offshore winds with a 7 5 board. The board looks too long for that condition though.
With the small board you can see the lack of projection but plenty of speed (and a surfer that know how to s)
Few years ago I asked Bill his consent to make and try but no customers decided and I have been out of the water due to damaged body so still I do not build one.
I have some ideas though like using bigger boxes to use them advancing one to have more grip or hold in bigger surf etc
I think that closer the feeling is more like a single fin. The Purchase separated ones would feel different.