I prefer not to use the Frixxion pens, they are not designed for use for quilting. I first found them about 5 years ago and contacted Pilot, the manufacturer. The customer service representative couldn't tell me if they were archival quality. Quilters have gone nuts over them and I think Pilot has found a niche market for these pens, so of course now they claim the ink is archival.
I actually prefer to use products that are designed and manufactured specifically for marking on fabric, such as tailor's chalk. My one exception is soap - I will sometimes use a sliver off of a bar of soap to mark dark fabric.