I have one but haven't used it. I have a serger. From what I understand, it trims away the seam allowance & zigzags over the edges. A serger KNITS the stitch/seam making it stretch. It sews the seam, trims the seam allowance & overcasts the edges in one swipe. With 4 threads, it also sews a safety stitch seam too.

I have a side cutter foot for my Brother machine that I have used in one project. First of all, it took a long time to figure out how to use it, even with the 2 or 3 pages in the manual explaining it! I used it to make a simple 4-seam skirt with an elastic waist, and after a few washings the seams came apart. Not the stitching...the fabric unraveled. I never knew if it was the fault of the fabric or the side cutter foot, but I haven't used the foot since. I have a basic (inexpensive) serger that I use now.

Donna