I have one, and I used it for awhile. Then I decided it was just as easy to stick with my machine. I have a Pfaff and the instructions for it didn't wind the bobbin correctly. Somehow I remember that it did the bobbin backwards. Once If figured that out, I was able to turn my bobbin over and it worked fine. Just more trouble than using my machine.
My sister uses one all the time to wind her long arm bobbins. That's sort of why I bought one. I was new to quilting and she was very pleased with hers. So I thought I should have one.
Dina