Only filters the air thru both - so both cabin air (Recirculated) and the outside air are filtered using that same media - so if sticks, pollen, sawdust, sand, carbon old oily exhaust - dandelion seeds and other whatnots are getting pulled in, then that air is repulled back thru that same debris field no matter if it's recirculated or fresh.
So moldy or not, the Microban used in the filter media is only able to work only for so long, until it gets overloaded and simply can't work and do the job it's claimed to do, kill or reduce mold. (Microbial)
I too felt that same way and pulled mine - have not been disappointed with those results - seems there is little backpressure or holdup in flow - would rather wish to have the older outside vent pull knobs like the older days - but it (this setup) gets me by.
Kinda had to do this all along for other needs of the passengers - one had asthma and low tolerance for molds and mildew - it would affect her breathing and if not corrected, could put her in a hospital and even be life threatening.
Fresh air not recirculated - for if the carpets or panels or any sort of fabric had mold, odors, exhaust or CO2 or some type of mildew or contained an allergen they can react to - it can seriously affect their health if recirculated brought that back into the air - so even with Microban and its limited life span and cycles of use - easier to leave the outside air open all the time - safer too.
When you look at this from an operation perspective, the wet days using such a filter media - was like asking for trouble to be continued into the subsequent days of drying out afterwards - it doesn't last for a day, it becomes lifelong for the life of the vehicle once in the carpets, upholstery or ductwork of the vents - it's extremely hard to get rid of - just short of direct replacement - and who has the time, money or resources for that?
Gives you good conscience to review titles of many of todays used cars that were salvaged from floodwaters.
You can catch more of my thoughts about it - here...
https://www.fordfiesta.org/threads/new-to-the-group-have-ac-clicking-issues.7552/post-17838
https://www.fordfiesta.org/threads/heater-core-mk7-fiesta-manual-climate-control.8315/post-21330