An independent air source has several advantages over the standard octopus. Being independent, you can simply hand it off to the diver who is low on air/out of air. The huge safety factor is that you are not attatched to him/her as you would be if sharing a conventional octopus. Another advantage is if you experience a problem with your scuba unit, you have an air supply totally independent from the regulator/cylinder where the problem is occuring. A good example of this woudl be a 1st stage high pressure seat leak, which will affect both your primary regulator AND your octopus. Spare Air is the smallest complete scuba unit in the world. Since the regulator and tank are one unit, you just pop it in your mouth and breath! Nothing could be simpler, and simple is best in any emergency situation.