I haven't noticed super fast growth in any of the Ageneiosus cat species, I'd say slow to moderate growers. They like to swim in the current mid water level most of the time however occasionally just sit on the bottom completely still. I prefer to keep mine with a sand substrate to mimic more natural habitat and have kept Ageneiosus Magoi, Ageneiosus Marmoratus, and Ageneiosus sp. in the past. I generally fed earthworms or other various live foods, never found mine to be that interested in pellets.
As far as tank mates go, anything that can't fit in their mouth and isn't too aggressive works. I'd aim to keep them with other smaller SA cichlid species