Carbon fiber blades are more fragile or as fragile as fiberglass ones. Plastic blades are more durable. At least in theory.
Nevertheless, walking with your fins on on a rocky beach is not acceptable
If your intention is to spear between rocks 10 or 12 m deep, the blades will not do much difference; so get the cheaper ones.
If you dive deeper (like 15 - 25m) regularly during a session, then you may consider fiberglass or carbon fiber blades. It will help.
For good ratio quality/price fins you can check also
https://www.leaderfins.com/
For performence CF blades CETMA , C4 and other manufacturers.
The fin is the extension of your foot and to work perfect or as expected a few parameter must must come together, like comfort of the foot pocket, stiffness of the blade, blade angle and shape, fitness level and personal preference, fragility (an important factor if money DO matter !).
Good luck with your choice!