I love how the rubber-coated feet handle chiffon and satin and other slippery fabric. Replacing them is $20 a pop, but you don't have to do that very often.
Terry at TnT knows all the vintage Singer slants better than anyone I can think of - if you need anything for your 400, 500, 600, 700 series or later machines, he's probably got it and he's fast and easy to deal with, too. He's written his own repair manuals that are absolutely incredible. Here's his Futura page:
http://tandtrepair.com/Futura.html