Work surprisingly well. Simplicity, functional, effective but on first outing while removing my scarf one valve popped open and the diaphragm fell out. My order for replacement was filled promptly and I'm more vigilant now that I'm aware it can happen. Maybe offer replacement diaphragms.
These masks are very comfortable both from a breathable and comfort standpoint. The valves are easy to lose. I suggest getting extras.
Sports Mask - Valves
Love it!!!The valve release keeps the mask edge against your face.
Very satisfied with the valves.👍