I have both feet for my Bernina 430. I bought the #57 when I was still fairly new to quilting because I needed the guide for accuracy. Now, however, I find that I can't always see whether the fabric has slid under the guide and don't quite trust it the way I did at first. I bought the #37 recently (can't recall the price, but they're all expensive) and use it more than the #57 now.
Anita