Yep, I have an Xblock ruler. We used it in making a retreat quilt.
Unfortunately the person direction us on the use of the ruler didn't know enough to be able to accurately tell us how to use it.
I learned more when I went on a Shop Hop and one of the stores was demo-ing it. Main thing I came away with was to iron your seam flat. At the retreat the trimming of the block was awkward because the ruler kept tilting various ways. Had I been told to iron seams flat, and yes I did ask this question for everyone to hear the answer ['whatever you want - it doesn't matter'], I wouldn't have had so many problems squaring up the finished block!
There are lots of pics online. You could also try a QB search.
ali