Not exactly on topic, but good info about respirators with valves for general COVID-19 protection:
https://www.fastcompany.com/90496717/what-is-a-mask-valve-and-why-are-cities-banning-them
Summary in case you don't want to click:
When you wear a mask with a valve, a significant portion of your exhalations are entirely unfiltered. When you add the valve, you aren’t even filtering your breath with cotton. Your mouth is essentially an open exhaust. Good for protecting the wearer; bad for protecting everyone else.