What can y'all tell me about these? Does anyone use them? Are they easy to use? They are 2 for sale on craig's list in my area for $50 and I was thinking about getting it with my birthday money but I don't know anything about them. The seller's say that it will work with any home sewing machine. I'm very interested but don't want to spend all my money if.........ya know. What are y'alls thoughts?