I recommend against green tea extract, but especially against decaf green tea extract, for several reasons. Yes, tea is healthy, and there is science to back this.
But tea is mainly a healthy beverage, not a medicine. Its health properties are frequently over-hyped, especially by companies selling extracts and supplements.
Many people are stuck in a "green tea is good but caffeine is bad" mentality which is just not backed up by science. The reality of things is that a little of many things are good for you, but too much of anything is bad. Green tea is no exception. Caffeine is no exception. The decaffeination process not only removes caffeine, but also removes antioxidants.
Also, the benefits of tea, whether green tea or other teas, are not limited to chemical effects. The process of drinking tea can be relaxing, and thus beneficial to health.
I'd stay away from the extracts if I were you.