Hi folks.
I found the Cosmo floss with an old DMC wool skein. And here's the result of comparing to the dmc black.
The feel is nicer, the black is sharper. Not a noticeable difference in the completed stitching on two letters, but the Cosmo seems smoother with less fuzz.
Overall, it seems smoother, more consistent, stronger. Cosmo is made in Japan, 100% cotton, by Lecien Corporation. I have all dmc colors and won't be replacing them, but may order certain colors for specific projects. Not a big difference really, but I will continue testing this black skein (next project has a black hat) since this one was quite limited.