The quality of these is horrendous. Looks like the first four that ever came off the line. Fabric sticking out of the frame, not adhered to the side, wire mesh all bent out of shape, pleats all jammed together. The only 'MERV 13' thing about these is the fabric. The way they put them together will never allow it to perform.
The quality and price are great, but the smaller measurements are problematic. The 20x20x4 (actual measurement 19 3/8 x 19 3/8 x 3 5/8) balances precariously in the slot it's meant for, I have to keep checking to make sure the airflow hasn't knocked it off kilter. The name brand I've used previously fits snuggly.