[Pastor]

The carbons cause less fatigue. Most of the Mediterranean spearos use carbon fins for deep spearing. On the same hand I think many of them use that efficiency to extend their bottom time. With fins like the Millenniums, they suffer from localised stress points, see those lighter patches around the top of the blade? It's a bit like gun rubber loosing its power after an extended time loaded. Over time the plastic looses its properties and becomes less efficient, this is temporally exaggerated in a single dive because of the localised heating from friction (admittedly this is very small but it all adds up).