Rubber straps have also proven themselves in diving practice, as they adapt perfectly to the changing pressure conditions under water. But metal watch straps and textile straps are also very popular on diving watches.
A helium valve, on the other hand, is only necessary if the watch is to be taken on dives to several hundred meters and the diver is in a pressure chamber during the decompression phase. This usually only applies to professional divers.
A helium valve is not necessary for amateur divers. On the contrary: a helium valve is then just an additional opening with a risk of leaks.