It is a filter combined with an activated charcoal filter. MSR used to sell something similar. I bought a Camelbak Groove water bottle with an activated charcoal filter. My idea was to treat first with my steripen and then drink it through the filter to improve taste/ reduce harmful chemicals. I am not a big fan of drinking through a straw so it doesn't get much use. Plus where I hike the water is tastes pretty good.
Activated charcoal is great at removing all sorts of stuff that is harmful to you like pollutants and heavy metals, however how effective it is is not well defined. I wouldn't depend on it to drink otherwise undrinkable water.