Hey,
It is really tough stuff. You have to take the little knobby root out with the plant if you don't want it to come back on you. I got an uncured box of Sargassum... er I mean Figi rock and I hated the stuff
It's a pain reaching into your tank and pruning the stuff back all the time. Although, do like the look of a couple long stands here and there I don't think its worth it. I forget all my research but you might want to look at seeing if they sporalate when they grow big, I would look into that.
And to my knowledge they don't have any toxic effects from pruning. Even with caulerpa thought to be toxic when pruned I never see any ill effects. You will be fine.
That stuff grows mad under good lighting!
HTH