it's called a "personal" air filter for a reason
I would not recommend sharing these, as the mouthpiece you have to cover to blow the smoke through is very large, and there is a small chamber between the mouthpiece and where the filter starts which very quickly collects moisture and saliva; furthermore this small chamber before the filter will hold a small amount of smoke which will release into the air if you do not first inhale through your nose and exhale a second time through the filter to get the last bit of smoke to go through.
Rating: 4 stars