I use them in my embroidery machine. I bought a whole mess of them (I think I got a gross; 144 of them) on Amazon for cheaper than I could buy that many empty bobbins. My embroidery machine uses the same bobbins as my 2 "backup" machines so I can use the bobbins again in most of my machines. (Unfortunately not my main machine though)
I wind my own for quilting, though, because then I'm using lots of different colors (and I don't know if anybody even carries pre-wound Janome bobbins). But for embroidery I only use white so it made sense to buy a pile of pre-filled ones. And despite them being super cheap they seem to work just fine - zero complaints so far. (But I don't use them a LOT; I think I've only gone through 5 or 6 so far so there could be surprises ahead, you never know. But I pretty much have a lifetime supply at this rate even if a few are baddies.)