I use to have the Scubapro MK2/R295 and Octo R295, they are the same regulator, except for one being yellow and having a longer hose. That being said i dnt see why u couldnt use it as a primary. Some octo’s dnt breathe as well as a primary but u are still supposed to be able to use it and breathe thru it. I have seen divers who use an octo as a primary also. Dnt see the need to STOP and wait till u get ur primary fixed. Might not be broke, Maybe ur octo is a great breather and u use an air source as ur octo or u have ur primary hooked up to a different rig and ur just configuring ur gear this way for ur current circumstance.