I have kept a sebae (seen in my avatar) for over a year now. It has really grown in the time I have had it...from approx 4 inches across to about 10-12 inches now. It took a while for my clowns to stop hosting a leather I had & move in to the sebae, but since then they have been very happy. I've had pretty much no problems with it at all. It quickly settled into a spot and has been there ever since.
One thing I have read is that sebaes don't normally split like other anemones, and so far my experience has been just that.
If you're looking at them in the LFS, try to avoid the ones that are very white, i.e. bleached...a good healthly one is usually more tan/brown and very 'sticky' when touched.
hth & good luck!
rob