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.
I bought these refills for my husband and myself to use. We really like them. The brush heads are firm, but not too stiff, they last a really long time, but actually tell you by way of colour change when they are due to be replaced.