You don't need to worry much about the long bobbins. The very early winders need to be polished and clean for the thread to move evenly, but most post 1910, or even before that have much the same winder mechanism as some class 15 and 66 bobbins (controlled by a cam action). They vary slightly from model to model. The only thing to worry about is getting the correct replacement shuttle and bobbins if they are missing to start with. 15 bobbins hold more thread, but if you find a nice VS machine there are ways about it (widing a few bobbins at a time). They are not more cumbersome to use when you get to know them.
Most of the old cast iron straight stitchers came in a treadle version, and there are nice round bobbin "non-Singers" as well.