While green tea can indeed contribute to fat loss, I would not expect any noticeable results just from the green tea, or green tea extract. Obviously, the green tea extract will be more effective, as it will have higher concentrations of the active substances. However, given the fact that it won't be all that effective for fat loss, I don't see the need to buy the supplement - just drink green tea, and enjoy the taste apart from its effects.
If you want something effective for fat loss, I would rather consider such compounds as SARMS as Cardarine GW and SR9009. These will burn fat, and they will drastically increase your athletic performance, which will contribute to even better fat loss. The good part about it is that in spite of their effectiveness, they will not cause side effects.