I use the frixson pen all the time. (spelled wrong.. but it is the iron off one.) The only thing I have to say is test it out on your fabrics first. I had one medium toned fabric lighten up at the place where I used the black one after ironing. It didn't matter on that quilt, but like I say test on the fabric you are using.
There are a few more colors available now too I noticed. I haven't tried any but the black.