Steel tanks provide more negative buoyancy than Aluminum. For example, you will need to add 5 lbs of lead to your weight belt to achieve the same buoyancy with an Al80 as you would get with a steel HP100.So, I have seen lots of talk about steel tanks, but very little on aluminum, is there a reason that steel tanks are so favored over aluminum for this type of diving? I also have to wonder what the difference in longevity is between steel and aluminum.
Steel also lasts at least twice as long as AL given even minimal care (i.e., rinse after saltwater dives, store somewhere dry, and keep at least a couple hundred psi in the tank so water can't get in).
The only real advantage of AL for single tank backmount is initial cost.