Yesterday, I got the boards for the latest revision of the layout (2017-10-24), as now available via OSH Park. I just assembled a new prototype and can confirm it works like a charm. It works best with 2.5 - 5 W, but can be calibrated to also work with 1 W. The only downside of the simple design is that the calibration is accurate only for the same power level (or at least within a narrow power range).
As for winding the toroid, use enameled wire no thicker than 0.22 mm for the secondary winding, otherwise the 25 turns won’t fit well. Make sure you only occupy ca 270 degrees of the core, otherwise directivity might suffer.
When ordering the parts, it may make sense to add a few 100 Ohm / 2 W resistors, for they make for nice dummy loads for various SWR levels.
I hope this tiny SWR indicator will turn out useful for many of you and will save lots of final transistors.
As for the ease of assembly: The board is pretty small and tightly packed with components on both sides. It should not be your first SMD soldering project. But then again, all parts are 0805 sizes and the pads optimized for hand-soldering. Take your time and a good magnifying glass
73 de Martin, DK3IT