I am new to the air filtration thing but recently been having some slight irritation whenever i wake up so thought of getting an air filter system. Just wondering, how effective is this kind of thing?

I see so many different air filter system but not sure which one is which because each claim they have best technology and features. I saw my friend using this small medklinn air filter thing and another friend use a damn kow big one - i think it's a sharp.

So how come one so small and another so big but both also air filter system? Confused ler...