Why does Unicom change cats for free?

It's not completely free, but it's free during the warranty period. Unicom broadband light cat can be replaced free of charge during the warranty period. However, if the equipment fails due to water ingress, lightning strike, man-made damage and other reasons, it is not covered by the warranty, and the replaced light cat belongs to non-new equipment. The warranty period and policies will be different, depending on the local business hall.