I had a Red Devil in a 100 gallon with an albino Oscar, a Jack Dempsey, pleco, and two large Bala sharks.
Everything was fine for a year(?). Came home from work one day and I had one fish in the tank. The Red Devil. She had destroyed every other fish in the tank, it looked like someone had run them through a wood chipper. Even the pleco.
She is a beautiful fish, but insane.
I would only keep a Red Devil by itself. Very....hmmm....Personable(?) fish. The Devil seems to recognize you, swims to the front of the tank, and gives an acknowledgment like,"Hey, how you doin' that my other fish lack. It has people it likes and dislikes. Kinda like a little barking dog.
Oh and it has grown huge teeth. Seems to have two sets of chompers and the outer set are large and sharp. And now that She is at least a foot long She likes to attack you when you clean the tank. My wife has named her 'Molly". If Molly breaks the skin one more time, Molly is going to have an accident. I am assuming its a female because it doesn't have the forehead bump associated with males.