I have used this 4" filter since replacing our furnace (used 1" Filtrete filters before this). Love how it cleans the air, especially since we have 2 Balinese cats. 

The only "con" about this filter is how hard it is to remove from the furnace. I finally figured out a way to attach a string to the front of the filter so that it's an easy pull-out when it needs to be changed. Perhaps Filtrete could come up with something like this, or 2 finger holes for easy removal. [This review was collected as part of a promotion.]