I buy the plastic sided bobbins (polyester) from Long Creek Mills for embroidery and the cotton sided ones (I remove the cardboard before using) in my long arm and have had absolutely no problems. They do carry NEBs for the best price I have seen.

I have used prewound bobbins with cardboard (plastic does not work in any of my machines for some reason) with success in both my DSMs and my shortarm (I sold it recently). I have quite a collection of prewound bobbins with beautiful thread colors from Superior Threads. When I bought my Bailey LA, I found it uses Class 15 bobbins. Not to worry! I simply use the bobbin winder to transfer the thread from the L bobbins to Class 15 bobbins as needed for any project on hand.

I use Superiors pre-wound bobbins for piecing with cardboard sides in my Juki and my Babylock. No problems at all. I love them and the thread. If you're Leary buy pkg of 10 and try them. I just bought a 1/2 gross this time because I go thru them so fast.

A friend with an embroidery machine ordered the wrong size of prewound bobbins. There were 100 of them! They fit my Pfaff, and so far, no problem. The bobbin thread is thinner than the top thread, and it actually seems to help keep the 1/4" when quilting to have that thinner thread. All of these are white and I use the prewound on everything except really dark colors.

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

I use pre-wounds from Superior threads almost exclusively on my LA. They have so much more thread on them than those you wind yourself and they are wound so much better. If you wind on your machine while you are quilting, the winder starts and stops as you do. This makes for uneven winding on your bobbins which can give you tension problems. I need the size M but please do make sure you buy the size you need for your machine!

I have a Janome and a Juki and I use cardboard side bobbins all the time without problems. I also mix the thread types . So does your longarmer.

I see in the picture that the Super BOBs are M style. They wont fit in a domestic machine. Your need L style. Ms are larger for some longarms.

I only use pre bobbins on my APQS long arm, and Superior bottom line. I have also used them on my machines. I have never had a problem with the cardboard bobbins.

I have had the same thing happen to me. I won't go that route again.