As for diving in current, I'm not referring to a case of going against current on purpose. Normally, i'll drift with the current. However, I have encountered on many occasions where two strong current on opposite directions meet and start to go downwards. I was holding on to a rock and flipping around, battered by the two currents. In the end, I had to swim hard against one of them into a sheltered bay.
What I mean by strong current is that when you turn your head sideways when swimming against it, your mask will be pushed around and your reg tend to flood.
The very plus point about the split fins is the speed with lesser effort, which in rec diving doesn't seem to gel too well. If you are going rocket fast, what are you gonna see?
Wouldn't good control and stability, with good performance against current and on surface a better factor to choose fins? As for finning on the back, that's pretty much what I do on the surface ever since I took off my snorkel. Does anyone else with split fins have problems on the surface finning on your back?