I agree with all this said on the Singer 15-91 by Kwendt.
I have one and I love it! It is awesome! My dh paid $20 for it in 1975 and brought it home to me. Just the best machine. I just might have to buy another one now for a spare! To FM is just easy peasy! A real tank!
I might add I have other machines, but this one stands out in the crowd!