My 37 came with my machine...and I do use it, but a couple of years ago, when my Bernina store was having a sale on feet, I bought the 57 foot...and I use it the most now...really like the guide when I am going to be doing lots of piecing...especially as my eyes are tired by the end of day...the guide really helps me sew straight.
It really isn't that much more than the 37 foot when you think about how much it will help you...so I suggest you get the 57 foot if you can afford it.