I picked up the GoPro 3-in-1 Mount just a few days ago and, while it’s a great tool, it’s a little pricey at $70. Functionally, it works quite well. The way the arm is adjusted, you can configure it so that the mount/arm is not actually in the shot. It will also fold flat to just the grip so that you can securely hold a GoPro at arm’s length.
The downside of using an extended arm in a video like this is that any motion is magnified even further because the camera is at the end of the mount, which you can see in some of the shots in the video.
The saving grace is the fact that GoPro camera angles are so wide that most of the shots are still very usable. Additionally, using slow motion when shooting 720/120p or 1080/60p allows you to smooth out some of the camera shake as well.