High-concentration glutathione reputation
Many buyers purchased specifically because glutathione is a trending, well-regarded brightening ingredient and this product is perceived to contain it in unusually high, effective concentration.
Repurchase / loyalty
A very large share of reviews are 2nd, 3rd, or even 4th+ repurchases, with buyers stocking multiple bottles during sales, indicating strong repeat-purchase behavior.
Word-of-mouth and recommendations
Several reviewers say they bought after seeing recommendations from friends, family, or online reviews, and then recommended it onward to others (including buying it as gifts for mothers/sisters/friends).
Vitamin C alternative for sensitive skin
Multiple reviewers chose this product as a gentler substitute for vitamin C serums that previously irritated their skin, citing no irritation even on sensitive or reactive skin.
Bonus/value pack size
The 20ml+7ml bundle and 'gift' mini bottle are repeatedly mentioned as good value, encouraging purchase especially during promotions.