For years I used a single edged razor blade for ripping seams and I sewed clothing for the public. Now I use my small Olfa cutter, pull the seam apart as much as I can and touch it and the threads part company with the item. The little white handled cutters that came with my machines take forever, wish I could buy single edge razor blades. Have to be careful no matter which you use, I have cut myself with them many times.
Carol J.