Very poor choice for this size of tank. Once/if it gets established it will make the meanest damsel look like a cake walk. Very few Pseudochromis species actually have a "community" temperment and should be kept with large aggressive fish. This guy will also get to about 2½-3" in size which a 12 gal
will not properly house long term.
Do you have a larger set up with less docile species it can be added to?