I have the pair of Lepidos with 5 Guianacara geayi, 4 Acarichthys heckelli, 2 Barumbi mbo Africans and 3 Synodontis petricola catfish. The Lepidos seem oblivious to those tankmates. I don't know if something similar shaped and colored like some of the Parachromis would appeared a threat or be threatened.
The Lepidos are not really aggressive though, they are ambush predators (strike and retreat).
They do get large, but slowly, I saw a photo in a Buntbarsche bulletin (June 2008) where a wild caught ones head looks to be almost 6 inches, so it may have been over a foot in length, and had barracuda like 1/2" teeth.
My pair is still fairly young, male 7" female 5".
Heckelii is singing that old song
"If you wanna be happy
For the rest of your life,
Never make a pretty woman your wife,
So from my personal point of view,
Get an ugly girl to marry you."