I had a chance to try a set of these in the pool last night, and I was much happier with them than I thought I'd be. They have a very odd, "trampoline" feel which took some getting used to, but after a while, I started to kind of like it. It was possible to do all the kicks in them, although it's clear that frog kick is not the OPTIMAL kick for these fins. But flutter kicking was effortless, using the rebound, and after a couple of experiments, the back kick went pretty well. They are very long, so you really have to control them carefully to make sure they go where you want. They are also very, very light -- I use plastic fins with spring straps in the pool, but these were MUCH lighter, with a noticeable effect on my trim.
Anyway, my take from a brief tryout is that they aren't cave diving fins, but they're MUCH better than split fins for students, because they DO allow you to use your fins as stabilizers, and they offer the same advantages of an easy flutter kick.