i got a nice clump of the awesome green centered ones about 2 1/2 years ago, and they never really grew for the most part.
every now and then, i'd see a quick growth spurt of a runner and a couple polyps form whenever i did something to the tank, like added carbon, added a skimmer, added a new light.......usually something major that changed the nature of the tank.
but other than that, they would mostly just accumulate a rough/hard, maybe coraline algae on them to the point the bases were very brittle.
i believe i finally lost them this past spring, and just ended up giving them to someone to see if they could revive what little polyps were left.
i would love to try my hand at them again, they are really cool. but i've heard mixed reports on how to keep them. i've always gone under the assumption of low light, low/med flow. but just recently the LFS i got them from, told me theirs are thriving under high light, high flow.
......so really, i have no clue. this is the only coral that i've kept that has me completely stumped.