I am a regular green tea drinker.... I'm not sure what to tell you about the studies, however I can tell you that from personal experience, I have noticed its effects. I don't think I would say it helps me relax, however it does seem to help me focus. I think that may be due to the way your body metabolizes the caffeine in it.
The antioxidants are a definite plus, since I started drinking it on a regular basis, I have noticed a change in the way I feel.... I tend to have more energy, and less health problems (IE: Colds, flus. etc....)
I'm always a little weary about studies, however for my personal opinion, I would defiantly recommend it!