Amazon calculates a product’s star ratings based on a machine learned model instead of a raw data average. The model takes into account factors including the age of a rating, whether the ratings are from verified purchasers, and factors that establish reviewer trustworthiness.
Came with all the pieces (Wear sensors, metal clips, grease) which saved a lot of trouble, and was even wrapped up in a blue shop rag. They fit great and were not hard to get into the clips. One thing though, the wear sensors came put in backwards (look at the pic I took before I knew). That caused me some trouble, but easy enough to remedy once I realized it.