Another consideration is that most species that show up in stores must be provided with a terrestrial section. Lacking one, and sometimes even with one, they will climb anything they can to get out of the water, and frequently escape the tank--usually resulting in a dead crab some days later.
IMO, they do best in a species tank, where their needs can be specifically addressed, and fish aren't endangered. If you decide to add them to a aquarium, avoid any long finned companions--bettas, guppies, serpaes, ect, as these flowing fins will be nipped and trimmed.
