In our family we have Mares Volo, Dacor Panther (same style as Volo with hinge in the middle, same Patent) and Avanti Quattro. Just for the record the buckles for the Volo and the Panther are now identical since Dacor got together with Mares.
Basically we find that the hinged fins are more efficient at low to medium finning speeds, cause less cramps and less air consumption.
BUT in an emergency, the thrust & speed is just not there.
In one situation where I had had to fin really hard to tow an almost unconscious diver away from waves breaking on some rocks, the fins just hinged to 90 degrees and I didn't go anywhere.
When I looked at the fins after the event they had formed white stress lines right across on the line of the hinges. They didn't crack or break and I am sure I will still be using them for a lot of dives, but I now know their limitations.