AB5: The problem is the oil in the filter.
Most aftermarket filters flow better than paper ones, because the filter element isnt as good. Clearly the size of the smallest particle that can get thru the filter is proportional to the amount of effort you need to draw a set amount of air thru the filter.
Aftermarket filters tend to use an element with much bigger gaps in it, to provide the "freeflow" but becuase this obviously has a detrimental effect to the actual filtration they try to get round this by impregnating the element with oil. The idea being that the small bits of crap will stick to the oil as they pass thru the large holes.
The problem stems from this oil being drawn thru the filter into the airstream and contaminating the air flow meter. You may never have an issue, or it may die inside a few weeks, it really depends how oily the filter is and what state the AFM is to begin with.
Lots of "performance" modifications out there are popular, but when you actually analyse them, they offer little or no benefits, and quite often can be detrimental to the car. Its just all marketing hype, and people that THINK they know what they're talking about informing others how amazing mod-x is.