This is a glimpse of the interior surface of the leading edge tube of a Best Waroo Pro HP. It has cuben fiber on the inside of the middle third of the leading edge. It's actually a great idea. The cuben is actually a pure spectra laminate that is simply amazing. I personally use it in many of our own kite designs. This is the main closure seam of the leading edge. It is perhaps the most important seam on the whole kite. It takes the most force and is often one of the first to fail. It's not because they are under-built. They are actually quite strong. It's just that the forces involved can be amazingly powerful, as any of you who have been lifted off the water know. This seam has signs that are classic of having been over-inflated. As you can see here the fibers have actually moved over and started to unweave. This was not evident until I opened the leading edge up. It looked like it was just a tiny section of the leading edge that was having problems, but it turned out that the seam was weak down a section about 2 feet long. Keep in mind, I think Best Waroo Pro HP stands for High Performance, not High Pressure. You still have to inflate these with care.
If you look closely in the above picture, you can see that there are fibers that are running diagonally. This is because the cuben fiber is made on a table, not on a loom. Thus they can get away with running fibers at any angle, not just 90 degrees. You can also see that the cuben fiber doesn't quite reach out all the way into the seam far enough to be structural. This I think is why this section failed.