To calculate the overall star rating and percentage breakdown by star, we don’t 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.
According to my wife (for whom I bought it), it is very efficient to prevent colour fading and keeps the hair well hydrated. From my side, it is quite an expensive one, but at least it seems to work very well.