Products like these are difficult to review. It's the same with vitamin supplements where the effects are also difficult to point to. That being said, I'm very happy with these GTE capsules. My primary reason for buying them was to cut down on my daily intake of tea; too much tea may discolour your teeth, and since I already drink a lot of water, 2-3 cups of tea would have me running back and forth to the bathroom. I'm loving the convenience of the GTE capsules. If you're used to caffeine, you won't feel anything from the small amount they hold.
I don't feel any different when taking it, maybe a small caffeine boost, however stacking this on my previous cut helped me to shed my body fat right down! You will get a metabolic increase as intended.