So this is what we did: after fully topping off our test RAS units using the manufacturer-recommended fill method, we took them down to a depth of 60 feet, which is generally accepted to be a typical diving depth for today’s average recreational diver. Then, after using one breath from our primary tank to clear the RAS second stage, we counted how many breaths we could get off each system using consistent three-second inhalations. Once these capacity tests were completed, we returned to our own tank, and breathing at the same three-second inhalation rate, and using, as consistently as possible in a real-world situation, a 30 feet-per-minute ascent rate, we counted how many breaths it took to reach the surface (as it turned out, it took 16 breaths).
While not scientific, and without taking into account air expansion or contraction due to shallower or deeper depths, these breath counts for air capacity taken at 60 feet, coupled with a breath count for a standard ascent from 60 feet to the surface, provide us with a picture of the relative air capacity of each system and how close to the surface each might be able to get a diver. Hopefully, this info will help you gauge whether one, all or none of these redundant air systems would suit your individual diving style.
I found the write up ridiculous! The "stuff" above sounds like a 3rd grade science fair experiment.
I've been trying to follow some of the SGR releases, but this one almost ranks up there with the glowing review of the bladed dive light...