This is a very well made labour-saving device that reminds us of a time before knives were made of stainless steel. After World War I, household cutlery was one of the first products to be mass produced from this new material, saving a lot more labour. 

Knives are frequently exposed to acidic foods, and even light rust resulting from this can dull a knife’s edge. Hence it was the knives in particular that needed regular polishing in the days before stainless steel was perfected, and a mechanical knife cleaner would have saved much time and effort in a large household.

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Kent's knife-cleaning machine was popular during the mid-19th and early-20th centuries before the invention of stainless steel.

Since knives were exposed to acidic foods, they had to be cleaned and polished dialy to keep them form rusting and becoming dull.

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Easy-to-use machines like Kent's saved much time and labor, earning them the label "necessary."  They were so helpful that one female education manual cautions against allowing girls to use rotary knife cleaners because the luxury will make them inflexibel and indifferent as a housewife