CEA are not entirely herbivores, and get less so as they get bigger. When they get above a certain size, they will attack the tetras. I think the firemouths will be all right.
CAE will clean surfaces like walls of aquarium but they can get aggressive. The SAE will clean algae off plants and crevices and are peaceful. They do different things in an aquarium.
True SAE will stop eating algae once the get full grown but they don't have the sociopath personality of the CAE. The CAE are just a lousy critter. False SAE are good for planaria outbreaks.