I have tried FM on the 401 - I just like the clone better - maybe it is the foot.
If you want to sew knits get a gold band needle - it might do better - yeah the patterns only go one direction - not so good for stretch.
I just sold a machine last night - it was a Phoenix. That one had a really neat FM foot setup. It had a little lever on the back of the machine - did a great job of FM. I originally wanted to keep that machine but a little gal came along and it just seemed like a perfect match for her. I'm thinking she will be very happy with that one. The more I saw of that machine the more I loved it. I have my Singer 403... and a herd of others.