I have used a Volcano before, and I own a Vapir One. I bought the Vapir about 3 years ago, and I really haven't found much use for it. I think if I owned a Volcano, I might use it a little bit more. I did find, however, that the novelty runs out quickly. I usually only have the urge to use it if I have people over (once again, for the novelty of it) and when I am really low on weed. It seems to be pretty efficient. The Volcano is fucking expensive, though. If you are thinking about buying one of your own, I would recommend thinking long and hard about it.
S-Town