No wonder the Neanderthals went extinct. Sea shells are NOT good material for tools. They are brittle and break easily. The modern humans used chiseled rocks for tools, which work better in butchering killed animals and last longer.
I’d guess the shells were maybe used to flesh or carve tender hides (rabbit? body tribal markings?), rather than butcher tough cuts. Neanderthals were a creative lot - surely their talents weren’t limited to a few cave paintings?