I bought a couple of containers of class 66 prewound bobbins. I have an adaptor so I can use them in my Babylock, which uses a different size bobbin than the rest of my machines. Not sure what it is . . .
Most of the large quantity prewounds come for machines that do embroidery, since you can really go through them fast that way. But then if you have a seperate winder, you can wind bobbins while the machine is doing it's thing.
I'm going to be purchasing a seperate bobbin winder, as I had to disable the electronics for my Juki 2010 and now I have no bobbin winder on it. It was either that or pay $400 to get the electronics fixed.