I bought this because I don't need to charge it. It's always in my camera bag. I mainly use my DJI Osmo gimbal, but GRAVGRIP is convenient for shots on the go and really easy for crane style shots.
Gravgrip is really good for low/high camera transitions. I get some awesome b-roll shots with my cell phone and their extension pole. Fast action shots is definitely better when my gopro is hooked up.
Definitely install the little gear they include for when using with cell phone. This made all the difference for letting my phone rotate smoothly. Overall very happy, I just wish I knew to install that little gear when I first set it up. It does mention it in the user guide, but I missed it.