As a book collector (I have that same 1st Hemingway!), I can understand why someone would want to brush their books all the time. It’s like grooming a horse. But to have a specialized tool for it begins to reek of book-madness. My books are up so high that I can’t see the dust on them, but that doesn’t mean I don’t worry. The booklike back of the brush means it can hide inconspicuously among your volumes, and the brush itself has crenelations, although I doubt they really help that much.
Too bad this little objet costs $80! I think I’ll fill out my shelves instead.