I have 5 or 6 in my 100gal fuge. They go nuts when I drop scraps of fish in the tank, or a cloud of thawed brine/mysis. They are very fast snails.
I've started to target feed my two serpent stars, or feed them stuff off of a skewering stick lately since the nass. snails are so aggressive for food. They have a long foot which is like a slime-trail body. When they attack a piece of food they encapsulate it somewhat reminiscent of an octopus making a 'tent' over prey. Its gross looking but cool at the same time. Often two or more encapsulate the same scrap of food (leftover silverside heads, etc).
I have a handful of big mexican turbos and one conch in there also and so far the tongan nass. haven't bothered anything.