No build up of dust and cat hair in the furnace. Have only had them for less than a month but know that they are of good quality as our daughter has been using them for over a year.
The filter itself was fine.Took over two weeks to get, even with numerous calls. they said they would expedite them and I would call again to find out what happened and again they said they would get them right out.If you aren't in a hurry, then it's okay.
We recently replaced the Merv 13 Lennox replacement filter in our furnace. I've got to say, it sure does a great job cleaning the air we breathe in the house when you look at how filthy the filter was after 6 months! It made a believer out of us to always use a high Merv rated filter in the future.