Smart move on the idea for letting green tea soak overnight.
On the other ingredients in Zingers, the following is what I've found (credit: Wikipedia)-
(1) Stevia: is a somewhat controversial natural sweetener, which some studies suggest applications for treating obesity/high blood pressure;
(2) Hibiscus: claimed/debateable health benefits include digestive applications, treating bladder infections, nausea and high blood pressure; and
(3) Rosehips: high in Vitamin C, (17002000 mg per 100 g) and contains vitamins A, D and E, and antioxidant flavonoids. Claimed remedy for bladder infections, dizziness and headaches.
In summartion, green tea appears to be the major beneficial component. The others, if they help, great, if not, oh well. Otherwise the best part of this product is the convenience, cheap cost and the taste.