MMA fighter Justin Wren left the octagon and for the past 5 years has been fighting slavery and oppression in Africa. Wren has helped dig wells for clean water, grow & harvest food, and buy back land that was taken from the Pygmy people. He’s also working to replant trees in the areas deforested by companies seeking to exploit minerals there. He stopped fighting people to start fighting for the people. A true hero, indeed. source
The GM-17, and it’s upgraded version, the GM-18, were basically just filters attached to a facepiece. There were no inhale/exhale valves, although the ones that survived to be used in the 20′s and 30′s often had exhale valves added onto them.
Overall, they were said to be uncomfortable, but well designed, as the user didn’t have to use noseclips and a mouthpiece like with the SBR masks used by the Allies. Fogging might be an issue though, as there is no guided airflow, and the spider gaskets (meant to prevent cracked lenses due to artillery strikes) might hamper your attempts to wipe the lenses off.
I don’t think donning the mask would be very complex, it would likely require a deep exhalation after donning to insure that no gas particles remain free-floating in the mask.
Getting a Repro one isn’t too hard, I’ve seen some floating around on eBay in the last couple of weeks. It would require some additional work to make it actually look good though, including darkening the leather and beating up the metal a bit.