I bought the tank dies, and I'm glad that I have them. However, you can get the same results by doing a light countersink after the holes are dimpled with normal dies. I used my deburring scredriver (i.e., a 3/32" countersink attached to a power screwdriver), and it worked as good as the tank dies. Obviously, the tank dies are a single step solution, so this would be the better way to go, but countersinking saves you $30.
Tracy.