they are not 'rare' but their import is limited and tank propagation is fairly new for this coral so they cost more.
I have 2 and I do feed them individually, along with the babies that sprout off.
I think they are definitely worth it. they are unbelievably bright colored, and they are open all the time, where as normal sun coral is more nocturnal.
being that they are non-photosynthetic, pretty much anyone can keep one,either in a low light tank, or under a caved area in a stronger lighted tank.
If you have the funds, and the time to feed them, go for it!
heres kinda a crappy pic but these are mine....