I don't think Sidewinder makes bobbin winders for size M bobbins, and that's what most longarms use.
The bobbin winder that came with my Innova works great. I think they have provided different types of winders at different times, due to availability. I do have to make sure it's lined up correctly to wind the bobbin evenly, and it's a pain to re-thread it so I pull the new thread in by tying it to the previous thread. I also have to use a thread net on the spool if I'm loading poly thread on the bobbins, and if I go really fast the thread net flies off and there's a mess.