I use them but with care. I haven't had any that don't work however I have had certain colors leave shadow lines on certain fabrics. The shadow lines were almost like the ink had bleached out some of the color when ironed.
I like using them to mark seams and such and for general writing in my sewing area in case some actually gets on the fabric in the process I know I can get it off. I never use them to mark a quilt top for quilting based on my experience of the shadow lines