Depending on your setup you will see 10-30% range gain. But for me more important than range is quality of the video link (video is smoother and will break only at the end of range). I am using it all the time.
Have you used it with firmware 3.08 and the latest smartphone app?
I used the booster once before the firmware and ios app upgrade, but have been holding off until some official word that it is compatible.
Phantom is updated to latest and greatest updates. Stock without app: 1300 ft vertical before loosing video. With booster app: 2300 ft before loosing video. Real world back to back test. I'm happy!