I've been using the plastic bobbins for years and except when I drop one and then step on it, making it wind up in the circular file, and have not had a problem. I also have an older Brother machine which uses metal bobbins and have not had a problem with those; but I've never interchanged the two. I just keep a bobbin case for plastic bobbins and one for metal bobbins, they don't take up that much space.