Spare Air™ - The Dive Otter

A Spare Air™ is nothing more than a low cost pre-configured Pony Bottle, so we can use one of the Minimum Reserve Gas calculations to determine if the Spare Air™ is a viable tool for scuba diving.

Since it is unrealistic that you will share a Spare Air™ in an emergency, we can assume this is for you only and not a buddy. To determine the gas we need for an emergency direct ascent we can use the Rock Bottom Gas calculation for one person under duress:
(1.0 RMV * Average Depth * Time of Ascent) = Cuft needed

Which Pony Bottle Do I Want?

Tank/Bottle	Price	Capacity	Max RBG Depth
Spare Air™ 300	$400	3 cuft	15ft
Spare Air™ 600	$550	6 cuft	30ft
Standard AL13	$850	13 cuft	60ft
Standard AL19	$900	19 cuft	75ft
Standard AL30	$950	30 cuft	105ft
Traditional AL40	$1,000	40 cuft	125ft
Standard AL80	$1,000	80 cuft	>130ft

My Opinion

I just do not see how a tank smaller than 19cuft is viable as an emergency air supply. And given that Spare Air™'s largest tank they sell is 6 cuft...I can not in good conscious recommend one.