Together our dive team always run through the gear checks, of which both regs get breathed off of. I much prefer a nice breathing reg for my bungee backup, as it is mine, but I also like to have a knob to detune it so it doesn't free flow when not in use which is 98% of the time.
And they say there is not need for buddy breathing practice anymore...what if? I think it is a great skill to build confidence of not having a reg at all times and getting used to passing one around.
Usually rental regs free flow, but you found the one that doesn't work...a good reason to own your own gear right there.