Some of mine got to over 3in long. Ugly tan color. They pull completely off the rocks if you pull with a sustained force rather than a jerk. I use stainless steel tweezers to grip the stalk near the base really good and then, pull. They pop off and sometimes come off in clumps (if your lucky). They smell terrible, so watch out.
They also release junk into the water, so just prune a little at a time and run carbon. When I first started the war against them, I was messy and careless. The tank got a bit cloudy and then things started going nuts. My corals closed up, fish were breathing heavy, and hermits stopped moving.
I had to quickly do an emergency PWC
(thatll teach you to have water ready!) and go buy carbon. (Yepp, I was really unprepared) Later that night everything calmed down. Corals were open and fish were acting normal.
They wont spread if you banish them to the sand bed. Mine started there on a tiny piece of rock. I then thought it would be good to put this rock on the rest of the rocks.
I wouldnt consider having these unless they were an outstanding looking kind and had a large sandbed. (Which I dont).