i agree with Dawg- had a little brass mould which came with the first BP gun i ever bought- a .36 Navy. it makes ball and conical (not very good at either one, but i suppose it would be a whole lot better than nothing).
when i was young and poor, i used it to make roundball, but never got much use out of the conical... now i'm older and poor, so i bought a plain old two cavity Lee roundball which works much better.
if, on the other hand, the dual mould works for you, go for it: do what works for your needs, cast up a bunch of projectiles, load her up and
make good smoke!