are you guys diving with fins like these?
fins have improved dramatically since the 1960's
you may want to look into something a little more modern.
those look designed for a pool, a long time ago.
Newer may be better for you and others, but it doesn't mean better for everybody! Fortunately, people have choices in this life and everybody doesn't have to follow the crowd when they move inexorably and expensively from one technology to the next. I, for example, choose not to own a mobile phone and I've managed perfectly well without one.
I subscribe to several vintage diving online forums, whose members often speak of encounters with non-vintage divers (we nickname the more outspoken of them "the scuba police") who will generally, and not very originally, say "that stuff will kill you!" when they see our classic gear. Well, we're still alive, me in my 60s and others with the same interest in even more senior years. We're a conservative lot and we take the view "if it ain't broke, why fix it?" A few younger divers and snorkellers do join these groups in search of something different, a gentler way of life. And it's wrong to assume that just because many or most people in the west have moved over to composite fins, the rest of the world must have followed suit. The Japanese still snorkel and dive on the whole with all-rubber full-foot fins (Gull Mews etc), which they manufacture in their own country, and they would take it most amiss if you dismissed what they have on their feet solely as "pool fins". If you prefer your fins made from modern synthetics, good for you, I'm glad they match your requirements perfectly. However, each to his own, and I'll stick to what I prefer too.