I would like to find a walking foot with a metal shank. The plastic shanks are the first thing to break for me, although I have had the whole thing fall apart also. Once I found a penguin WF at an estate sale for a couple of dollars. It was dysfunctional, but my friend was able to attach the little spring inside, and it worked fine.
Right now I have a slant WF that works perfectly on my 301 -- I just hope it lasts. The last two that I have purchased for my short shank Pfaff 130 have not worked correctly. It seems to be trial and error to me!