the problem i've seen with those pens is---yes the ink disappears when ironed--but then it comes back when the item gets cold- so if you are using them to mark a quilt- be prepared for your lines to be back if the quilt ever gets cold.... mark lightly- it can be quite heart breaking to have a beautiful quilt all finished and then have marks appear out of no where- of course you only need to (re-iron) but seriously- who wants to have to iron their quilts all the time? and do you put that on the label if you are gifting the quilt?...if lines appear on quilt-just iron with a hot iron???
they may seem like (magic) but they sound like a pain to me- i'd rather use something that actually goes away- instead of something that is just disguised for a bit of time...under certain conditions.