Da_Man, it's not "purely aesthetic". He will always flip it around to fight with it, but he holds it like that to defend his rear and so that he can concentrate more on his Force powers.
Juno, Form VI is Niman. That's not a reverse grip style.
And Maris Brood is the same case as Darth Maul-she uses a style that can be extremely dangerous to untrained wielders, but she has mastered it enough to avoid this danger easily.