To calculate the overall star rating and percentage breakdown by star, we do not use a simple average. Instead, our system considers things like how recent a review is and if the reviewer bought the item on Amazon. It also analyses reviews to verify trustworthiness.
Great so far, I like the convenience of being able to track heart rate without the chest strap. Battery life is about a week usage, with 3 runs clocked - 2 x 5km and 1 x 12km. Phone notifications is turned on during the day.