there are two types of porcelain crabs: anemone and "non anemone." One has a lot of white, has a curled up abdomen and is kind of awkward in its gate while the other is maroon and grey striped and very quick with more of a flattened body. I've kept two of the non anemone types (maroon and grey striped) with no problems. You may have to target feed them meaty foods to keep them longterm. Mine disappeared after I stopped doing that.
The anemone ones (a lot of white, curled up abdomen and an awkward gate) tend to be a little more sensitive. Seems like they rely on the anemone for health.