A few months ago I purchased a steel 120 cu. in. cylinder or tank from a friend. I wanted a steel 120 tank because it can hold a lot more air, about 3600 PSI compared to my aluminum 80 (80 cu. in.) which can hold about 3000 PSI. With that extra 600 PSI in about 30ft of water I do a two hour dive with my camera and still have a nice cushion for the return trip. With an aluminum 80 I’m surface swimming back no matter what.
Here’s a quick picture so you can see the difference. The blue tank is my Aluminum 80 and the steel tank is my 120. The 120 is about 10 pounds heavier and a little bit taller.