I have a 2.7 cu.ft one the size of a coke can but since I bought it before I learned that I really need a 13-20 cu.ft tank to get back up from a 100ft depth safely I’m still OK with the unit. I still find it useful to have as a safety air source while on the surface - I can get a 30-40 puffs from it when using it on the surface. I do recreational diving so the pony tanks would not fit my needs yet.
Charlie