In theory, green tea extracts are great skincare ingredients because they contain powerful antioxidants (polyphenols). Tea plants can contain impressive quantity of the four polyphenol types: ECG, GCG, EGC, and EGCG (the most powerful in the pack). Unfortunately, these water-soluble antioxidants are very unstable. EGCG, for example, requires a low pH (below 4) to maintain stability, and a formulation with such pH can be irritating. It is degrades under influence of warm temperature, UV light and air. Looking at the formula of Zelens Tea Shot serum, I suspect that no particular effort went into stabilizing the green tea antioxidants, and this is why I doubt that this serum is effective beyond providing hydration benefits. I do not think it is worth the price tag. If you are after an antioxidant serum, I would recommend choosing a product with 10-20% of ascorbic acid and using it before its color turns to yellow/ orange (the change in color of the vitamin C products indicates that the ascorbic acid has oxidized and is no longer very effective.