A good FFM will have a gas switching block so you can switch to a redundant gas source, however, you are still using the same demand valve (second stage) built into the mask. In the case of a demand valve failure, it would be mask off, alternate gas source in (be it an additional DV on your rig or a buddy's octopus) and conventional spare mask on.
The problem with the gimp mask in the picture is you cannot use a conventional second stage with a mouthpiece, so your planning has to include either a personal bailout with a second stage with no mouthpiece, or your buddy diving the same mask with his regs rigged in the same manner. If you are diving with somebody who doesn't have the desire to look like an inflatable sex-doll, between you, you'll need to think what he does in an OOG situation.
I am a strong advocate of always diving with a spare mask. What do you do in this situation? Do you carry a normal mask in a pocket, or another gimp mask? If you are using a conventional mask, you need to have an alternate gas source with a mouthpiece available
Another issue is the mask is forming part of the seal on your gas supply. What happens if the strap fails? Normally you will continue to breathe normally, and either reach for your spare, replace it if you are fortunate enough to catch it or have it handed back to you by your buddy, or you make a calm, controlled ascent. If the strap fails you are now have the mask issue,
and an OOG situation to deal with.
I have seen these on the internet before, but I've never seen one in the flesh. I see some advantage for cold water divers, but this is far outweighed by the many negatives. Most of my diving is in cold water, and I've never seen anybody use one - if I had, I wouldn't be here to type this as I'd have spat my reg/loop out with laughter and drowned.
If anyone does plan to use one of these, remember one important thing...
"The safety word's 'banana'!".