Standard Monofin tail vs an extended tail ( H2o & Splash )

[MarkF]

In H2o, Mako, Aquamarine and the first Splash the fluke has a 10” or so extension making the feet up inside the tail. On the bottoms of their feet is a plate which a flexible rod connects to the tail a distance down. Does that work? Does anyone know if this was a good swimmer? Luno Makes a Monofin and Orca which are extended.