Just think of your octopus as a piece of backup life support equipment, rather than just yet another piece of equipment that you're required to lug along. If something happens to your or your buddy's primary reg, one of you will be depending on the octopus to stay alive. You want it to be a good, solid, quality piece of equipment. It doesn't have to be an equivalent of your primary 2nd stage, but should be capable of delivering decent performance and reliability. Majority of generic cheap octos you see out there fall short. Invest in a decent one. You can typically get a very well-performing octo (a lower end Mares since that's what your primary is, ScubaPro R380, Apeks ATX40, maybe one of the Oceanic models) for less than $150 if you shop around. I'm sure there are other manufacturers that make equally capable octos. Hope this helps.
-Roman.