Although not the most versatile stabiliser I've ever used, the Opteka's advantages are the rigid, U-shaped structure that is brilliant for filming sports in particular. If you're following a skier or skateboarder for instance, you can grip with one or two hands and point it easily at your subject.
The frame doesn't do much to increase stability apart from allowing you to bolt the camera down to the grip and use your own frame to keep the tracking smooth. I found it fine for filming skiing but for other, more bumpy sports it wouldn't be great.
It's pretty darn cheap so the value is amazing for what you get, I paid about £20 for it.
Here's a video taken with it without any stabilisation added: