ART's are truly magnificent fish.
However pretty much everything you hear about them is true.
Each indvidual fish is different & you occasionaly hear of tales where they have been kept with other fish and are ok but generally they are out & out viscious.
Anything they cant fit in their mouths they will just continually bite & harass until they kill it.
Ive been lucky enough to have a few.
My 1st one was half the size of the other cats it was kept with in a large heated Pond & more than held its own but other than territorial squabbles it wasnt too much trouble.
Bear in mind however this was a 16" fish in with some Big RTC's, Vulture Cat, L.Mammoratus all between 20" - 28".
My current one is approx 10" and it really is the devil in disguise!

Was " temporarily" in with a Big 20" G.Gourami and it would hide by day & harrass the hell out of the GG by night so had to be moved.
Bear in mind this fish can exceed 39" (1 metre) in length it truly is a beast of a fish & deserves a species tank only.