...The old Singer darning feet are quite rare aren't they, I have never seen one in the flesh.
One came with my black cast iron 201, but it was missing other bits again. I need to track down two tiny screwdrivers, I would like to complete the accessory box on both of them :- )
I did read that the aluminium body 201s are not quite so suited to the heavier work that the earlier cast iron 201s can accomplish, so I have made a mental note to not sew anything too heavy on her.
It's only the body that's cast aluminium, all other parts are steel, forged meshing gears, etc, exactly the same as the earlier version. I think the reason why they say the earlier 201s handle heavier work better is because of the different hand wheels. On some it's a larger cast iron thing with spokes, some are a solid smaller cast iron wheel. The larger spoked wheel might have an advantage, but it's not a big deal. Either way, very little stops them, even the later version with cast aluminium hand wheel. The cast iron body would absorb more vibration and rattle than the lighter aluminium, but I don't noctice much difference. They feel a bit different though, even if they are much the same machine. If a 201 doesn't run smoothly, you know it needs cleaning, oiling or attention some where.
What usually limits the 201 (as well as a 66) is the hight of presser foot lift and needle size. These vintage machines takes up to size #22 (140) needle which is rather large. I would not push any of them too hard, but you would have to directly mistreat them to do so.