My boost fin took so long to get here, that I ended up going DIY foil drive route. Then a full efoil. How a $200 kickstarter dream becomes a $20k lifestyle shift
I haven't tried boost fit yet on a foil board, only longboard. The push is pretty weak, but is enough to get you planing on a wave you otherwise couldn't catch on the longboard. So on a foil, I expect it might add 10%, which may be enough to catch a wave that you just barely can't catch either prone paddling or sup. But beyond that "just barely" wave, I'd say not enough juice to get into unbreaking waves -- it's maybe 1/10th the power of a foil drive. Though also less weight, less cumbersome, so tradeoffs like all things. You'd have to ride high to keep the fin out of the water, I had envisioned cutting off the top half, but I think it houses some of the mechanism, antenna maybe, so could be risky to remove.
installing 2 would be a fun experiment. Though for the $1000ish it would cost, and a little elbow grease, you could build a Faux Drive with lots more versatility.