Faber cylinders made in Italy are the standard for dive tanks.
Steel offers significant advantages over aluminium cylinders due to steel’s much greater strength. This allows for thinner walls and smaller overall size for the same internal volume. Steel cylinders also have better buoyancy characteristics as aluminium tanks become positively buoyant as they empty and you must wear extra lead to counteract this whereas steel cylinders remain negatively buoyant throughout your dive.
The 3L Size works well with the KISS Classic and many other Closed Circuit Rebreathers.