Force fins require a different kick than regular fins. In the 1980, when I was Fin Swimming Director for the Underwater Society of America, I was sent a pair of Force Fins to evaluate. This I did in a local reservoir on the North Umpqua River. Here's what I found:
--Force fins require a hard down-stroke, and very little effort on the upstroke.
--The ease of swimming is for people who develop cramps from their hamstring muscles. There is very little need to use the hamstrings, as there is little propulsion from the upstroke.
--Any stroke will work, but with modifications, with the Force Fins.
--It is much easier to walk in Force Fins than in regular fins, due to the upward turn of the blade (newer, longer-bladed Force Fins were not evaluated for this).
One write stated here that the Force Fins were best used with a frog or modified frog kick. This really is not true, if you are talking about a "real" frog kick used in the breast stroke. That kick uses tho bottom, or sole, of the foot (and the bottom of a fin) for the stroke. If this were done with Force Fins, there would be very little propulsion, as the fins would simply bend forword more. But, if the top of the fin is pointed backward, with the toes pointed, then you will develop a large propulsion.
The sissors kick is not too great with the Force Fins either, as the foot going backward would have very little propulsion.
I found that either the regular kick, or the dolphin kick, worked well with Force Fins as long as the down-stroke was very hard, and the upstroke relaxed. On the surface, a person used to a regular kick using other fins is likely to break the surface and splash a lot with Force Fins, because of the lack of risistence on the up-stroke.
SeaRat