FWIW between my brothers and I (we used to run ~8 boats and ~12 OBs between us each season, small & large, fresh & salt use) have put fins or foils on a dozen or skiffs from 12' to 18' over the years. My boatclub also has a fleet of small skiffs (> 20 at the dock, size limit to 14' length) and I'll help other owners setup and maintain their skiffs and more than half wear fins/foils.
Once hulls get bigger and/or heavier, I really prefer trim tabs. Smart tabs would be an option for a boat from 18' to maybe 20 to 22' in length, HP dependent of course. But any bigger and Bennett trim tabs rule!
Here the benefits as I have experienced them firsthand, listed with the largest or best improvement IMHO:
-Keeps the bow down when rising onto plane - THIS being a huge safety issue!
-Eliminates porpoising
-Allows a slower 'on plane' speed, sometimes ideal when running in a tight/close spaced chop
-Makes the hull (smaller skiffs) less sensitive to trim, i.e., weight distribution fore to aft
-Improves stability while running or crossing wakes at a slight angle
-Improves tracking/grip in turns, less tendency to roll
-Improves fuel efficiency when the OB height is setup correctly [This factor alone should probably be closer to the top of the list, but I only confirmed on the 1 boat that had a fuel computer built into the GPS with realtime/instant values of gph and mpg.]
The only negative I have ever experienced is some loss of 'potential' WOT speed, but again - if the OB height is setup correctly, the foil or fin should be just above or at thr surface anyway, so in theory, any added drag should be negligible!
FWIW, through various testing from boat articles I've seen, the most efficient foil/fins tested were the SE200 and SE300 by SE Sport. IMHO do not buy or use the 'clip' feature - every one I've seen has always fallen off or let go sometime in its life/use ... If you are going to use one, bolt the sucker on ...
Link to SE Sport = https://www.sesport.com/5_32.asp