That was my concern also, I noticed no difference with the Cab Fresh and Scotty. I've even had someone watch while I hammer the boost up to 35 to see if the filter in the Cab Fresh defected, not a bit.
My decision was more like I had to use the Cab Fresh, many big trees in my area were clogging the vent system up. Cab Fresh works great, makes it easier to clear snow off the vent intake also.