Yes: this is a species that can starve in your tank pretty easily: they eat up most of their supply and starve before it can grow back. Some reefers pass them around for this reason. They do work on algae like nobodies business.
The ink, as noted, is also dangerous, though if you don't have particularly aggresive bullying fish/crabs, shouldn't be all that likely. And while it can be toxic, it's a lot less toxic than cuke guts (i.e. lots of carbon and a polyfilter and a water change added quickly can save your tank)