@Dr Herring you should be using a BOV, when you need to bailout you don't want to have to remove the whole mask if you don't have to.
Why are you wanting the FFM in the first place?
I used the KM-48 for cold water technical diving. With the nose and face portion of the mask separate from the oral cavity and its removeable pod, you have a different set of options than with a traditional full face mask.
With a traditional full face mask and a BOV, you'd switch the BOV lever to bail out and that would work for most bailout scenarios although a loop that is flooded and caustic can put enough caustic into the BOV when you switch to make that less than ideal.
With the KM-48 and a DSV in the rebreather pod, you'd have to close the loop, then remove the pod with the DSV in it to switch to your bail out second stage. That bailout second stage could have a pod or not.
Alternatively, you could have the rebreather pod with a BOV installed and just switch like you would with any other BOV. The added advantage is that if you get caustic in the BOV side, you can remove the pod, flush it all out and then re-install the pod on the mask. It potentially gives you the best of both worlds.
And as noted above, on the KM-48 you can exhale though your nose and vent gas out of the loop hands free, or close the BOV and vent through the BOV, or tilt the de-watering valve in the mask and exhale to remove gas from the loop that way was well.
It's very flexible.