The GB ultimate is another great plane and one I have never built. I have seen over a hundred of them i'm sure over the years, but when they was the in thing to have I wanted something out of the ordinary so I went with the sandbolt er I mean skybolt.
While it is a great plane in itself the Ultimate I believe is better. Have fun in both building and flying it.
One word of caution bipes don't fly quite the same a a single wing sport flyer.