I would like to train with the gear that will give me the best success at completing the training versus using something that helps with learning to fin but doesn't give you the real effects of the actual fins you'll be using.
The fin used to train doesn't give any best chance at completing training other than the fin being of quality materiel and manufacturing process.
Although ability of fin to propel swimmer through water can differ because of size of fins surface area and whether it's designed for surface or subsurface swimming the legs and feet still need to be conditioned for swimming with fins.
Long distance surface sprints with fins were of more importance for pararescue prior to development and use of RAMZ and other deployed by parachute or from helicopter motorized watercraft as swimming was only way to catch a moving target (space capsule, drone, survivor in one man or larger raft) prior to the mid 1990s.
Further other than during my assignment in Iceland I have never been assigned to a helicopter unit where SCUBA tanks, dive equipment and ML-4 kits specifically configured for pararescue use only were placed on the alert helicopter. At other units I accomplished water rescues either going into water with flight suits or BDU/ABU and no fins.