I love Steatocranus, and have kept those two and half a dozen others. They are rapids fish with reduced swim bladders - an adaptation to keep them from being swept out of their territories. They hate all other fish, but because they suck at swimming, they have never harmed tankmates here.
They are solidly grey, but are really interesting fish to keep if you have a high flow tank with rockwork galore. They do hide a lot, but come out enough to be entertaining.