Split fins are not a gimmick... they work. And work great. Every independent test has shown they are far superior to standard paddle fins for speed and efficiency. Perhaps their only draw back is until you are used to them, it is harder to do little backup type maneuvers... who cares. I go forward in life!
As far as which ones - the
Apollo Bio Fins are my favorite - and have ruled the tests year after year. Very flexible, no cramps, and yet more speed than any other fin if you want to get up and go to try to get a shot of the turtle speeding away...
Larry
http://www.scubatoys.com