Watching library authors struggle to support both Scalaz and Cats is painful. An example is the Argonaut project. Because many parts of the two libraries are different implementations of the same mathematical concepts, it is often possible to use implicits to translate instances from type classes in one to the other.
I’ve released a new version of my library that does this for you. I call it Harmony. It now supports Cats 1.0.0-MF and Cats MTL 0.0.2.