Its amazing how many people are concerned about out of air emergencies. Man, if you run out of air, you've got a bigger problem then the FFM being on your face. It takes 1 second to pull it off, it takes longer to find a back-up source of air from a negligent buddy.
I've been using FFM's for years, taught my underwater photography classes with them and am a huge proponent of using them. I've done frigid New England diving with them and would much rather dive with an FFM then anything else. Your dry, you're much warmer and there is never any need for mask clearing. Plus, its a lot safer then biting down on a regulator, ya never get any water in your breathing path. Yes, the added volume can be an issue for some people, but it never bothered me.
I prefer the OTS and AGA masks to anything else. The silicone sealing system works great against rubber drysuit hoods, total full seal and with a breather valve on the top of the hood for bleeding, you also get some warmth from the air coming in from the FFM. In warm water's, the FFM's benefits can be a bit more touch and go, the benefits are less for sure when the water temps are around 70f.