I've always been open minded on fins and over the years I've tried many different designs - including various split fins and force fins. But every time, for my kind of diving, I have gone back to Jet fins, or more recently the OMS Slipstream equivalent.
Split fins are easy to kick and allow a rapid kick cycle, but they don't produce much thrust, especially at lower forward speeds. They also don't have much of a glide phase with the high cycle rate flutter kick where they are most efficient. In a single tank configuration it does not matter much. But when a 200 pound diver has on 100-150 pounds of technical diving equipment and a drysuit, split fins lack the low speed thrust to get you moving with all that drag and inertia. And once moving, the slow frog kick and glide with a large pair of jets is more efficient and more sustainable over a 2-3 hour dive at a 50-70 fpm speed than are split fins. And with the extra drag of a tech configuration, doubles, stage, etc, split fins just don't get the job done in a cave, especially with a less silt producing frog kick where split fins are much less efficient.
Similarly, back kicks helicopter turns etc, have more authority with jets than with split fins, especially in doubles, and in a cave environment precision control is important.
And I am one of those people who maintain that split fins don't back up well. I do pool lengths backwards when swimming with no fins or scuba gear and as someone noted earlier, you can back up in a single tank with no fins at all. So before you claim the prowess of back kicking in split fins, try it with the fins off and see how much if any improvement the split fins really add.
