Flow seems to be the biggest problem with them, as Dustin mentioned. People have had a hard time replicating their flow requirements in tanks. Maybe they'd do fine in a public aquarium setting since they can get those big waves going, but it'd be hard to do in a home tank.
If you have a friend that has been successful keeping them, then you have a really good source to learn from. If you do end up keeping an achilles you had better post pics, because they are by far the prettiest tang out there, and a fish that I have always wanted! Back in my "noob days" I asked my LFS about them after seeing pics online, and my LFS was decent enough to tell me, "Sorry hon, you're not getting one of those for your tank." ;)