Panzer, if your passion for the sport is proportional to the number of questions, well that's a...good thing.
First:
size. The average length of blades for spearfishing/freediving longfins is 74/76 centimeters. C4 Falcon blades are 76cm, Merou Carbon are 78cm, Omer Rekord III are 74cm, Omer Millennium are 74cm...
The extra-long longfins (longer than 80 centimeters) are a different category (C4 80 and Vgr 81 et cetera), meant for "pure freediving". They're generally softer, and require a
wide kick , which is not always easy in spearfishing situations.
Those extra 10 centimeters in length can be really annoying for spearfishing (at least for the average reef inshore hunting). You'd better stick to the 74/76cm type, which are still in longfins category, rather than the extra-long.
Omer Rekord. I used to have those fins and liked them a lot. The stiffness is medium soft (between C4 25 and 30). Apart fromn the Norwegian site you mention, I've never, never heard or read anyone complaining about the Omer Rekords, and I've never heard anybody whose Rekords got broken or cracked. Very good spearfishing fins, IMHO.
C4 and Spetton are two different companies who just signed a commercial agreement: Spetton distributes C4 blades in some countries, with Spetton footpockets. I used to own C4 blades in Omer footpockets, and I've heard of people using C4 in Dessault footpockets....
Where to buy carbon fins: Yaffle!