I have a golden mussel, only had it for a few weeks though, I've been feeding him Kent 'Microvert' (horrible yellow liquid) out of a syringe straight into it's little siphon.
I'm getting some phyto too, so I can take him out and put him in a tank of the phyto every now and then.
Basically, they are very labour intensive for something that doesn't move much, I only have one because curiosity got the better of me, and I thought it would be an appropriate addition to an invertebrate tank. It digs in the sand every now and then too.