My thoughts are in the same line as .g.e.o. Where I sail I would prefer a board with two shorter fins and I would not hit the bottom as much as today. Is there a performance advantage or disadvantage?
Based on observations sailing with my buddy...
In B&F sailing, if your option is a single shallow fin or a double shallow fin, in marginal to just powered up conditions, the twin fin is substantially faster (15-20%) and points higher.
When the wind picks up to where the single fin is powered to overpowered, the twin fin is much overpowered and one needs to fin down (reduce fin size). If you don't, the single fin board outperforms the double fin board, but not by 20%, more like 5%.
It's what you would expect, if the twin fin is equivalent to a single but larger fin.
My objections are in other areas; in shallow water performance, light to moderately powered, the twin fin outperforms.