I never thought about buying them because I have tons of bobbins here and the fact I use vintage machines exclusively. But this has been around for decades they used to sell the bobbins for the Vibrating Shuttle machines pre-filled. (the barbell looking ones)
It is a neat idea but it does seem like a waste to have a plastic bobbin that you can not turn in. Seems like with all of this "Go Green" thing that they would offer a deposit on them like the old glass coke bottles. (Remember picking them up and turning them in for candy and comic books?)
Billy