My "Laundry Blues" quilt has oodles of half-square triangles, which I like to make slightly larger and cut to size (like most people, I cut more accurately than I press and sew...). The corners of my favorite "square up" ruler are getting worn so yesterday I went looking for a replacement. I'm normally not a tool junkie (fabric and beads are a different matter!), but I saw this and thought I would give it a try.
The gray strip running down the center is actually a channel cut in the backside of the ruler. It butts against the seam allowance and is supposed to be more accurate than traditional rulers because it doesn't wobble because of the bulk of the seam. I like the idea and use it for the first cut, but the measurement lines aren't quite where I would expect them to be for the second cut. If the lines are a thread past the outer edge of the block, then the final square measures true according to my other rulers. :-)
If you've used this ruler (an Australian import), let me know what you think.