They can be aggressive eaters, mine just choses to hunt pods all night and won't eat a thing... But he's growing and getting fatter, he's about 1" right now. Seems those big amphipods must sustain his gluttonous butt for hours at a time because he's getting girthy for something the size of a cigarette butt.
he is not cryptic or shy at all, he's out all day every day, doesn't hide at all -- But they're small, so they can be easy to miss.. I think that's where they get the cryptic myth. In a big tank with a lot of live rock, they'll be easy to miss. They get 2" when they're very old.. It's rare to see them much more than 1.25-1.5". It's not a big fish.
And yes, they are an anthias, but like hawkfish they perch and I *believe* lack a swim bladder. So they're pretty close to a hawkfish.
Lastly, they will eat any shrimp that will fit in their mouth -- and their mouth is small. Sexy shrimp will be hunted to death. Baby shrimp will be decimated. Adult or even medium size shrimp won't be bothered at all.