DIY air purifier under $100 is taking America’s classrooms by storm

The comparison works because the alternatives are worse. The incumbent is random air purifiers (glorified fans at 10X markup) from China with "proprietary" filters, compared to the economy of scale of generic furnace filters which have been sold at volume for many years, in standard sizes.

DIY enables making your own design choices. Instead of disposable box fans, inline duct fans can support high static pressure applications, they are available in a range of prices and reliability, with Fantech near the top end offering German motors in USA-assembled fans.