Review on 🚿 Aprilaire - 10 A2 10 Water Panel Replacement for Whole House Humidifiers 110, 220, 500, 500A, 500M, 550, 550A, 558 (Pack of 2) - Aluminum by Zach Sornsin

These filters are slightly smaller than OEM versions. This means you have to be careful when inserting them so they don't slip. It also likely means they aren't as efficient as the OEM versions, as air can flow through the filter instead of going through it. As the saying goes, you get what you pay for. I didn't have much money back then and a cheap filter was better than no filter at all. I would not recommend them as the best choice.