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.
Have been using a Braun series 7 for years and decided to give this a try. Compared with the Braun it's underpowered and is very difficult to get a clean and complete shave. Have used twice and decided to switch back to the Braun.