Magnesium anodes are available with several different chemical compositions,but in two basic generic types with voltage outpurts of approximately 1.55 and 1.75 voles( with reference to a copper/copper sulphate reference electrode)

The 1.75 volt material is an alloy specially formulated from pure virgin magnesium and other elements to produce the higher voltuge. It has several advantages over the 1.55 volt material that is often produced from recycled material. In particular,the higher driving potential may allow fewer anodes to be used for a given project.
Its higher capacity results in improved performance, wih the possibility of longer anode life.