</font><font color="blue" class="small">( Makbe us cheep skates can get one from a wrecking yard... )</font>
TractorLegend,
The whole point of these gadgets is to save money on filters by not replacing it until it is actually making the engine work for air. Replacing a filter by the way it looks is usually way before it really needs to be replaced. It should pay for itself in air filter savings.
And, BTW, they also make one for fuel filters.