Since I've not been diagnosed with any mineral deficiencies, I don't really feel the need for supplements, and I believe that if I eat a healthy and varied low carb diet I shouldn't have any need to do so. But it's a matter of personal choice.
However, I do use and have always used salt to flavour my food, but generally potassium and magnesium come from foods rich in these minerals, some of which have always been part of my diet low carb or otherwise, though I do currently use a water filter that contains magnesium.
Leg cramps that I suffered from years ago pre T2 diagnosis and which were caused by fluid loss from prescribed diuretics but rarely happen now, were also fixed by regular "doses" of potassium rich bananas; now if necessary I up my consumption of potassium rich veggies, some of which contain more than my old high carb banana stand by.