Potassium Metabisulfite (Kmeta) is more common. Both the Potassium and Sodium versions can be used to provide molecular sulphur dioxide to protect the wine but most people don't use sodium metabisulphite because the commercial wineries don't use it. Not sure why there is rules against it's use but there is and it's probably for the best. Less sodium in our diets is always a good thing.