Where have they been spotted?

[yogavnture]

I suspect the material cost is so high that even if you reduced labor cost by 4/5, they wouldn't sell in enough volume for an established manufacturer to bother. Especially since a) it's not easy to explain the advantages, you really have to try them and b) the "advanced" diver seems to want to emulate the tech divers' frog kick and paddle fins even in environments where you can utilize the more efficient flutter kick (in appropriate fins) without issues.

All I know is the material is same as roller blades wheel ....polyurethane...or something like that ...