I bought some too, but haven't played with them on fabric yet. Not to worried about any marks showing up in cold weather, as it would disappear with a hot iron. They do sound neat though!
I found a marking pencil kit by Singer today. Has anyone used this brand of pencils. No instructions with them, so am curious? Will test them on some scraps first, to see... Not sure how to remove the marks, any info would be appreciated!