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 this fitness band specifically for the swim tracking option. It does this pretty well although sometimes when changing from backstroke the freestyle at the end of a lap it doesn't register that I've started a new lap and I end up a lap down. The smart band functions re how it handles messages and notifications are very basic and limited, but that's not really what I bought it for so I can't really complain. As a cheap fitness and sleep tracker it seems to be doing a pretty good job.