  Every C*-algebra gives rise to an effect module and a convex space of states,
which are connected via Kadison duality. We explore this duality in several
examples, where the C*-algebra is equipped with the structure of a
finite-dimensional Hopf algebra. When the Hopf algebra is the function algebra
or group algebra of a finite group, the resulting state spaces form convex
monoids. We will prove that both these convex monoids can be obtained from the
other one by taking a coproduct of density matrices on the irreducible
representations. We will also show that the same holds for a tensor product of
a group and a function algebra.
