Organixx is promoting a supplement containing “Unique Full-Spectrum Daily Magnesium Supplement Complete with 7 Forms of Elemental Magnesium & Co-Factors.” They claim the seven varieties have somewhat differing roles among 300 known important effects of magnesium on the body. Is this true? Should everyone be taking this to maintain optimum health?

This is partially true. Some varieties are more important than others. For some, it is more a function of bioavailability to begin with in getting the magnesium salt absorbed in the first place. But there are physiologic differences for the same reason, that some forms are transported more readily into and through cellular compartments. So this is a complex discussion lacking enough information in your question to do it justice. We would regard this as icing on the cake but not the cake itself, meaning it's something nice to have but not the highest of priorities given there are multiple sources of magnesium in dietary substances as well as in many foundational groupings to provide vitamins and minerals for daily consumption. The body can make the forms it most needs, so there is more marketing savvy than scientific validity in the assumptions being promoted as some kind of breakthrough.