AP301/AP302/AP303 Air Purifier Replacement Filter, H13 True HEPA Air Purifier Filter for CADR 300+ m³/h Air Purifier, Activated Carbon, Original 1 Pack, White

I have been shopping for air purifiers for several days. This one looks real good and the maintenance cost (filter replacement) isn't too bad either. However, the write-up failed to mention one of the most important considerations in the purchase decision...how often to replace the filter. Two identical machines with a $35 filter would rate very differently if one filter was changed annually and the other monthly. Please make sure your advertising covers the important information.