I have used several different FFM with DH regulators.
In the past I have used the Hope-Page mouthpiece with the old Cressi FFM and I also have a US Divers old FFM that has fittings for either a single hose or the hoses of a DH. I still have both set ups with their own dedicated hoses, but haven’t used either in a while. I did not find the US Divers mask to be very comfortable. Actually the Cressi was probably not that comfortable either.
I now have the new OTS Spectrum mask and that is a very comfortable mask. I used it with and Argonaut and a DSV mouthpiece. It was comfortable and worked very well except when I was on my back. When the regulator is much lower than the mask, there is positive pressure on the mask. This mask is so soft that the positive pressure will lift the edge seal from my face and it causes a free-flow.
I have used positive pressure FFM before like the AGA mask and they can be ver nice, but you do need to have the mask adjusted tight against your face. I tried adjusting the Spectrum mask a bit and I have to try it again, but it is possible that the mask skirt is just too soft.
This free-flow issue is only when I am on my back and I can probably de-tune the regulator a bit, but that would not be my first choice. I tend to tune my regulators fairly aggressively, so this may not be as much of an issue to others.
Buceador con escafandra autónoma clásica.