I have been using the Merv 8 filters with success. I change every 2 months and also look at my evaporator coil. There is no dust buildup that shows that the Merv 8 is doing a good job of filtration. Good quality. Filter Buy responds almost immediate and receive replacements in a couple of days but I do reorder on the date that I replace the last one.
I was buying which seems to be the same filter from another company, and their prices are so much higher. Found shelter by while searching, gave them a try, very happy.