Amazon calculates a product’s star ratings using a machine learned model instead of a raw data average. The machine learned model takes into account factors including: the age of a review, helpfulness votes by customers and whether the reviews are from verified purchases.
Great all-rounder treatment to just use once a month and not worry about. Has a very strong smell once applied, and if you have a wriggly cat like mine it's hard to get them to stay still to apply it to the right spot deep enough in their fur. I've had no side effects though, and it dries quickly enough that if some gets on her outer fur while she's getting away and she tries to lick it, she's fine.