I used to have another machine sitting next to me to wind bobbins while I was sewing on another...silly huh? Then I discovered prewound bobbins. WOW, 144 of them at a time. Awesome! Be sure to select the correct one that fits your machine. Be aware that there are 2 sizes.
My Janome states that it is almost out of bobbin thread when I use a prewound but after checking you can see that it is not.
Ladies and gentlemen it is worth the money!