I loved them, but stopped using them due to returning marks. There was an article that stated the marks return when cold, so I marked several fabrics, ironed the marks away and put them in the freezer.
The marks returned as clear as ever. I washed the swatches twice and returned them to the freezer. The marks were fainter, but still there.
My friend said, "Who is going to freeze a quilt?", but if left in the attic or car during the winter (Ohio) I wouldn't take a chance.
I'm waiting for a product that will be so easy to use, but be very safe. No more Frixion for me.