Over the last several years most of the special ops folks, Rangers, SEALS, USMC RECON, USAF PARA-RESCUE have adopted the newer split fin techonology. They always use XL size for reals ops since they are wearing combat boots. When in training they order 3 or more sizes. These brave men do not care about scubaboard or brand names. We never use this info in our ads or promo material. I am a USMC Vietnam Vet. I have been diving since 1971. I have 1000+ logged dives and another 1500 or so unlogged. My first fins were Jet fins. I have had 15-20 pairs of fins, Voit Duck feet, Mares Plana and Avanti, Cressi Frogs, USD blades, etc. The split fin technology works. If you want to do a wide scissor kick, a dolphin kick, a backward kick. a vertical hold, just buy a stiffer version of the split fins. This past month we outfitted several special ops groups with bio-fins. They prefer the original bio-fin pro since it offers the least resistance and the most propulsion with all styles of kicks. If you know some of these folks you can verify it yourself. On the other hand, if you like your Jets, good for you. Lots of safe diving to all.