I would say that if you buy a small specimen, you could keep a Naso Tang. If it grew too large for the tank, you could adopt it out to someone with a larger tank.
My experience over the years has been that very often, the fish I keep, while healthy and active, do not grow to expected size in a smaller tank. I've not experienced behavior problems with tangs in other tanks unless I placed two tangs of similar size or body shape together.