Having taken a diving class back in '77 and learning that aluminum doesn't rust, but it does corrode, I became wary of breathing air from metal containers.
Surely the draft of an aluminum pipe becomes 'protected' by a layer of tar, eventually, but it's the idea that the metal might deliver more than smoke that concerns me.
Now, I know, there are other pipes with inner tubes that might be aluminum or some other metal that might be just as much concern, but I've not really heard much about these pipe's performance.