I have used GABA a lot and have had some great deep sleep from it... As for release of extra GH i don't know for sure but it has helped me better from daily workouts.
I take 3-5g around 15 mins before i go to bed to get a good nights sleep. Some people get tingles and shortness of breath from using it. This is harmless and subsides after around 5-10 mins. But if you dont like the feeling then just drop the dosage to suit.