Nope, not common. Yes they do work. They've been discussed here a while back, and over on VSS. There's a few of us who have or have had them though mine is the only one I've seen that takes cams. I wasn't all that interested in it until I saw the cam door on top. I wonder if a bobbin winder from a different machine would work. I don't know if the size of it's shuttle and bobbin is the same size as anything else.
Cari