Why would you buy a redundant air source when you dont have a primary air source? Get your basic gear first (regulators, computer, whatever) and learn how to use it. After that you can consider what extra equipment you want to get.
For now I rent air tanks. Our local dive shop doesn't rent pony bottles or spare air. If I need redundant air for safety then I have to buy one of these options. On another thread some people were saying that all you need to do is look at your pressure gauges and manage your air. I wish it were that simple and nothing ever broke...
I will think about what everyone posted.