My split fin detector went off, I detect the word split fin in this thread someplace.
Don't do it, they suck, I know I've spent more money on fins than some people have their entire rig, don't become a victim, some shops will fill your head full of stuff about them like, they are faster, prevent cramps, give you better air consumption, hell they even cure cancer, its all crap, don't ever let them touch your feet if you get used to them you'll be hooked on em like crack and you'll never see the light, just say no.
Sure they are faster if your swimming a 2 mile race at max speed, I don't get in the water to race, sure they won't tire you out as fast as standard fins if you get in and try to swim at warp speed, and they do a real good job rototilling up the bottom too!
Just don't do it man, they cost too much for crap, its like paying someone to slap you, why would someone do that? I dunno.
Get you a nice set of paddle fins, quatro's, jets, anything, just say NO to split fins please, if they give you cramps then kick different, modified flutter, frog, modified frog etc, I could strap plywood to my feet and not get cramps, seriously.
If I have offended anyone that likes split fins, well, I dunno what to say cause I"m not going to say I'm sorry, these are my opinions as I've had them on my feet and almost hurled under water they stressed me out so bad, I did a fin swap with my buddy at 40 feet cause I couldn't take it anymore, I've been down the OPV road too for you mares and dacor fans, those are also sitting on my garage floor covered in dust.
On a positive note, in a straight line doing a flutter for full speed they did provide good speed with little effort, but I don't dive like that, if you try to do anyting other than straight line flutter with them, well get in the water without fins and thats about how well they work, about the same as no fins.
I can give my opinions like this cause I've used them, if I could invent a time machine I would go back and save myself a boat load of money on gear by simply going back and giving myself the message, just say no man, just say no.
I know this isnt' a thread fin and I don't mean to hijack but this is the best advice I can give, seriously man don't do it. I've managed to convert 2 newbies from splits to a blade fin, they are now happier divers and they thanked me for showing them the way to scuba salvation.