I also have very mixed feelings about these pens. However, I purchased an embroidery pattern recently that recommended using them to transfer the pattern onto the fabric using a light box. I did an experiment. I do quite a lot of red work and had a piece that the original marks had faded out. So I used a red frixion pen to remark it. When I stitched it the marks were covered up. I will use heat on it-but it doesn't matter. So, when I do the new pattern I will use pens that match the color I will embroider with. I am very hesitant to use them on a quilt top for fear they will shadow or reappear. But, my solution is to use Crayola washable markers. I also use Elmer's school glue to make quilt sandwiches. I always wash my quilts and it all comes out. I have never had a bad experience with these products.