The Janomes don't like prewound bobbins.It is not recommended.

When I first bought my machine I bought a box of 144 prewound bobbins on Ebay - they were the wrong size! I wind the thread onto normal bobbins and I think they will last me for years.

I don't know anything about Janome machines, just Brother but I do know if your machine has a sensor to tell you when they are low it will not work because the sensor can't read thru the cardboard.
Someone said Janome doesn't recommend it so I wouldn't use them at all.

I HAVE A JENOME350 E AND I BOUGHT PREWOUND BOBBINS .THEY HAVE TO BE THE CLEAR PLASTIC BOBBIN PREE WOUND, NOTHING ELESE WILL WORK.. I TRIED,, LUCY