I never notice a smell with mine...but maybe if I had other treefrogs I would notice that one does have a stronger smell than the other.
As far as messy...Yeah, I think they are. Mine love to party. All night long I hear them moving around. They love jumping in and out of the water, and they get some of the dirt on them, and then put it in the water. IMO, they're big and clumsy and move a lot.