I sew on a Two Spool in a treadle, and love it. I was fascinated when I heard about them, and started looking for one I could afford. My first one, off Craigslist, is a beautiful machine, but lacks the all important spool "can", so doesn't sew. Fortunately I later found another one for sale, and brought it home.
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I had a jar of old wooden spools of thread, and received some with the machine, and yes, it does have a "bobbin winder" that will wind thread onto a wooden spool, although you have to guide it by hand. I wound the one in the picture. I think the modern spools are too fat, although I keep thinking I will take a spool with me to the store sometime to compare.
It makes a beautiful stitch, and sews as easily as any other treadle I have tried. I haven't yet figured out how to outfit it with a free motion foot for free motion, but finished a table runner on it this week.
[ATTACH=CONFIG]611316[/ATTACH]Paper pieced on my 99k hand crank, and quilted and bound on the Two Spool.
Like you, I wonder why this concept never caught on. Will be glad to answer any questions you might have.