Is it useful for bikers? With helmets?
For how long a filter can be used?
You can use every filter for 1 month. If regularly used.
Does it have metal on pose pin for comfort wearing?
There is no metal on nose pin for comfort.
What gases does it filter? Where are these replaceable filters available?
Automobile gases are filtered through its activated carbon layer in filter. Filters are now available on both Flipkart and Amazon.