My biggest complaint initially, is that the filter isnt actually 20 x 20 x 4. It is 19 3/8 x 19 3/8 x 3 5/8. It does not fit well in the space. I have yet to see how it performs.
I have already done a review, but said it was too soon for me to judge since I am still using the originally installed filter from the HVAC contractor. Maybe in 6-8 months I will have changed filters and seen any result.
tape this filter to a 20 inch box fan and it will clean the air in an average house about every 15 minutes. MERV 13 filter removes virus size particles. a 4 inch filter is less strain on the fan and allows more air flow than 1 inch.