I love my bungied backup, and despite what people say about never using an octo, I've used mine. I have fallen getting into or out of the water several times, and having that thing right under my chin to pop in my mouth has been immensely comforting. I honestly think this is one of the biggest pluses from that configuration. Donating the primary is great, but you can do that with an Air2-type rig. But it's harder, I think, to find your primary reg or your Air2 if you fall.