People either love it or hate it in their main tank. I personally like it, especially Cauperla racemosa (grape cauperla). Cauperla is the most common genus you see at your LFS. Your tang will probably eat this, although I have seen tanks with it, with yellow tangs, so I can't say for sure. Perhaps these tanks had enough of it so the tang couldn't eat it fast enough. That is another thing, this stuff grows like weeds. You will have to prune it back often if it is kept under the proper conditions.
There are other types of macroalgae too which you can occasionally find. Halmedia and Udotea are two genuses which have a calceous skeleton, but require very strong lighting to thrive. They will be safe from your tangs, but are harder to keep.
Other types include red algaes and I even have some purple macro algae (I have not heard of anyone who has this stuff. It is the color of the mat of green star polyps!)
As far as filtration macroalgae, especially cauperla, is pretty good. It soaks up nitrates and phosphates and provides more availible O2 for your reef. It is not as good as a clam or xenia at filtration, but it is still good. I would say give it a shot. And don't buy those plant rocks for $25, just get a free floating peice from your LFS, chances are they willl give it to you (this is how I have recieved all 8 species of macroalgae I have). Then stuff it between two rocks in a well lit area and it will start growin like crazy!
