I have worked extensively with using beryllium-copper alloy in various components and don't recall any special handling procedures in the factory for such materials. We used them in designing the casings for components that were exposed directly to salt water in under-sea telecom cable applications. I don't think anyone uses pure beryllium in any consumer product applications. I have little doubt Focal has done enough research to make sure it is harmless. This is of course all moot (for me) since I would never ever pay that much for headphones unless that was the only method I could listen to music for the rest of my life....
I heard the $4000 Focal Utopia Headphones yesterday
Very nice. Very expensive. Beryllium drivers. Reviews a bit hyped I think. Who would pay that premium otherwise? Not sure I could live just with any headphones still.