No, they're shit, they don't filter out poisonous gases, only relatively large particles. It's gases and small particles that cause the most harm and filter masks are useless at protecting you against these. Plus they will make your face horribly sweaty.
There is a guy who originally rode for Dynamo Despatch, but last time I saw him was riding for LDay, who wears a helmet, a gas mask and a pair of the 80s Oakleys. Wasn't that guy, was it?
Who was the guy who rode around with a snow boarding mask, knee pads and elbow pads, he used to crack me up? Also the young guy who wore an army helmet and had a track pump in his bag.
the guy with the pads also had motorbike style hand protectors on his bars which he'd made from cardboard. was the guy with the army helmet also the muppet who used to have a camelback as well? think he worked at cyclone for a while, wasn't popular, and was given a really damning nickname which I can't remember.