The end of the strap on my GW-M850 was very ragged. It appeared that two straps were molded together then cut apart, but not very cleanly. Using the info in some of the other threads here, I sanded down the end of the strap using 600 grit emery paper folded over a nail file to get a flat sanding surface. This did a pretty good job smoothing the strap end, but it ended up with a whitish haze when lit from the side. Polishing it with denim cloth smoothed it a little more, but did nothing to get rid of the whitish haze.
It occurred to me that coloring the end of the strap with a permanent marker might do the trick. A Sharpie Fine Point came to mind, but the normal black color is too black, and it shows a purple cast in bright light. I ended up using a Sharpie Fine Point in slate grey, and this did the trick. The before and after photos are shown below. When viewed from normal watch-reading distance, it looks excellent.
I thought I'd pass this along in case it's of interest to anyone else.