Yes the product spare air. For what you pay for one of those things you can set up a 19 cu ft pony with a real reg and regular spg or even button spg and have enough gas, for me anyway, to do a safe ascent from 100 ft including 3 minute safety stop. The spare air might be ok if you don't plan on going deeper than 30 ft and can blow off your safety stop. I never omit a stop. Yeah it's small and easy to carry but why? Have I ever had one? No. Would I use and trust one with my life in the types of conditions I dive and to the depths I do even solo? No, no, no. What it is is a can of air good for maybe 3 or 4 breaths at 60 ft. If I've been down any amt of time and need to abort due to a loss of gas I want enough air to get me up without omitting a stop and possibily taking a hit. Also you say you have never deployed it in an emergency, how many times have you used it in practice? If you've not how do you know it will work for you? To carry gear, any gear, and not be intimately familiar with it's use and capabilities is worse than not carrying it at all. Do you know you can safely ascend with it from 33 ft or are you willing to "trust" it. Exactly how many breaths can you get from it at 20ft, 30ft, 40 ft, 50 ft, etc. If you don't know I suggest you find out. I have had my 19 cu ft pony for over a year now. It has never been deployed in an "emergency situation". It has however been filled 6 times from my practice runs. And topped off a couple times for the same reason. In short, use it if you must but be sure you can use it in the conditions you usually dive in. If not ditch it and get a pony and practice with it.
