i already got some 3 L faber, which they have a round bottom, and also have some 3L aluminium with flat bottom alloy - catalina cylinders, but they are thicker in size makin my unit bigger which sort of gives me a harder time passing through tide places, ie, wrecks or caves.

Got any links to the ones you are mentioning? Also, do you think having flat bottom gives you any drag? thinking about scootering as well...