The Inspiration’s onboard oxygen cylinder charged to 200 bar will provide 3 x 200 = 600 litres O2. At the average 1 litre/min consumption rate - this gives 10 hours of diving!

Similarly, the Evolution’s tiny 2 litre cylinder will give 2 x 200 = 400 litres of oxygen or over 6 and a half hours of diving. Even if you had to work really hard on a series of dives and doubled your usual metabolic rate (to about 2 litres/min) – you would still get 5 hours or so from the one 3 litre or 3 hours plus from the smaller unit.