I heard they could be a bit buggy. I read the description of the bitter coast sound's file with the construction set and noticed a few entries for menu errors. Is this something to consider before using them? I'm particularly interested in Siege at Firemoth.

I've had BCSounds installed for a while now, and not noticed any problems. Of course, that doesn't necessarily mean there are no problems, I've just not noticed any. As for the other ones, I don't know. I'm sure there are plenty of other people here who are better qualified to answer your question, though.