well both have the issue (many times reported by me and others here) that they react on displacement in the material which is a real deal breaker for many effects.
so i hoped an edge based shader would do similar but ignore the displacement within a surface. (maybe optional like to use any edges starting with a certain phong angle)
p.s maybe this can be considered for future updates, if easy to add. it would make corona even more powerful and solve the old AO and curvature+displacement issue i think. best of course of Corona could find a way to fix these problems directly, so it works like v-ray dirt.