I used it on my wedding dress quilt because it can't be washed. Like copycat I used the Frixon pens for marking. My thread was metallic silver so I used the black pen and if there is still some of the plastic left behind, you can't tell.
Yes you have to be careful pulling it up, and yes if you have small sections its difficult but if chalk or other marking wont work its a great alternative.
Also discovered that a hair dryer works just as well for removing Frixon marks if the iron isn't practical (I had wool batting and plastic beads that I was worried about). Dad came up with that idea.