The answer to this question depends on (A) What type of metal you plan to cut and (B) How often/how much you plan to cut.
Carbon Steel blades can be used to cut the following: mild steels, aluminum, copper, brass, bronze, and other non ferrous metals. If you only plan to use your machine every now and again, or only have a few pieces to cut, a carbon steel blade will work just fine.
If you use your machine often and plan to cut a lot of material, we suggest using a bi-metal blade. The best way to describe a carbon steel blade is it is an economical band saw blade used for general purpose cutting.