I think defurrem helps to ease the furr through there system so it comes out the other end, if they have it regularily and so it stops furr balls.
I dont know if it works quickly but guess it depends on how much furr is lurking inside and whether they will have the defurrem regularily.
I know Misa has started moulting again but is also growing his winter coat, noticed it getting longer this week and that means moreeeeeeeeee furballs grrrrrrrrrrrrrr