I typically piece with white so I was filling lots of bobbins at a time - made the mistake (or was it?) of trying prewound. Now I'm hooked!! I found a supply of them for $10 for 144 bobbins (plus $7 shipping). When you figure the price, that's less than 12 cents per bobbin. They last longer, I haven't had any tension issues, and I am no longer winding bobbins for piecing! I'm totally in love!!