Here's my favorite darning foot for low shank machines:
http://shop.sew-classic.com/Low-Shan...t-SCF55417.htm
I've got a really big collection of darning feet, so I understand all about "the quest." LOL!
But this little $3 provides excellent visibility and smooth action.
I tried the Big Foot on my high shank and liked it well enough that I ordered one for my low shank machines - it's not here yet, but my money is on the underdog - pretty fair odds that the little $3 foot will do just as well or better than the $30 Big Foot. :)