WO diagonals are of different design/construction to the Bintel/GSO unit. The WO body is like a slice of triangular tube, with the sides attached separately, so the mirror position/angle is fixed and non-adjustable. WO claim that their patented design ensures perfect alignment of the mirror for the life of the diagonal. Full details are on their website:
http://www.williamoptics.com/diagona...2_features.htm
Myself, I bought the Bintel which is a beautiful piece of workmanship for the price and provided a noticeable improvement on the standard Celestron 1.25" prism diagonal in my N8i.