I used a double needle on a quilt. I didn't think about what the back would look like (duh), it was a zig zag and at first it was "oh, no!" but soon after the test piece I decided I kind of liked it. One thing to think about (I found out the hard way), is because of the zig zag, it pulls in the fabric, and so it will shrink your total size. Which you might say "that is pretty normal" but - if you have more horizontal quilitng lines than vertical, it means you are out of square! I worked and worked to get it square and it was really hard! I loved the fact I didn't have to do 2 lines, but could easily do it in one swipe (I was trying to get a quilt done that had been forever in the making, and was long overdue by the time it was ready for the quilting), and I really got to like the look and feel of the zig zag on the back - but I wish I had thought of the shrinkage factor before squaring up prior to the border, so I wouldn't have had to lose some inches. I don't think you could do a zig zag with the double needle, as it is as wide as the places where your needle goes when it zig zags - in other words the left needle is in the spot where the needle goes when it swings to the left on zig zag, and the right needle is in the right position. So, if you moved needles that are already in the extended width postition - you would be hitting your foot.