These are probably not the crabs you saw eating a cichlid... Many LFS carry Red Claw Crabs, which look similar but are brackish crabs, and a little bit larger and more aggressive. These are forest floor crabs from the foothills in Java. So, while they're ok with shrimp in the water, they need a lot more land area for climbing and burrowing. They spend more time on land than in water. Their claws can not open wide enough to pinch my skin.
Thanks msjinkzd for posting those links! The Red Devils I have are related to both the Vampire and Mandarin crabs in the links, but are still undescribed. It's been said that they are less aggressive than the Vampires, and they eat more meat than the Mandarins. Care requirements are similar for most Geosesarma crabs.