Not rare at all, just not as popular as some other corals, and difficult to ship (they have very sharp skeletons that can easily pop bags in transit).
They need good water quality, and moderately strong lighting. If you can provide those two things, it will likely do very well for you. I had a colony that tripled in size over about 2 years, and has produced 3 satellite colonies.
They dont Have to be fed, but certainly take small meaty foods- brine, mysis, cyclopeeze, etc, and that will help grow out quicker.
As mentioned earlier, they are highly aggressive, and can have huge sweeper tentacles. Sweeper length can increase in higher water flow, and decrease in slower, so careful placement in the tank can help cut back on some of the aggression. Just make sure there is enough flow to keep debris from settling between the polyps- if it sits and starts to decompose, it will kill off coral tissue.