your Janome machine most likely uses Class 15 bobbins.
most of the pre-wounds are Class L - whether paper or plastic.
although an L will function in a Janome, the 15s are best.
i love prewound bobbins.
they are not only convenient, they have much more thread on them.
i have purchased from this site several times.
given the price of janome brand bobbins and of Egyptian cotton thread, these pre-wounds also save money.
the bobbins were good quality and reusable. it's been a while because i bought a ton of them, so i don't know whether the bobbins are still re-usable.
the color selection for cotton thread is limited to neutrals, but they will work well for piecing.
they will also work well if you are quilting with cotton thread and can use a neutral color in the bobbin.
https://www.terradonembroidery.com/s...d_bobbins.html