Funny, I don't see how it couldn't affect a split more than a paddle fin. Have you ever looked at the videos of splits, especially the regular bio-fins, in action? If you get a chance to, I'd suggest you look at how open and angled the insdie edges of the splits are. Put sideways currents catching those exposed edges and it would seem to me that it would have to affect the split fin more, even if the overall effect isn't much to talk about (which I'm not sure we've determined yet).
Proabably few dives will only see nothing but cross currents the entire dive - most see the diver going into or out of currents, or no current, all of which splits exel in - but the original poster is asking his question as if a pure cross-current dive existed. I think we need to address that instead of writing it off.
Surface swims: Bio-Fins beat my butt out on surface swims, easily, as I use Rocket II's, but we may be talking two different surface swims here. One will be face down and snorkeling, the other face up, fins under the water a little more. We use the latter to kick out to where we want to be, then dive down to conserve air. I can attest to Humuhumunukunukuapua's experience that I will be breathing heavier, despite being in relative shape and being able to kick my stiff fins for entire dives, and that I would use a lot more air if I didn't wait to get my pulse rate down before diving under. I'd be willing to bet that if anyone claimed they weren't good on the surface, they meant for snorkeling.
