This pen was discussed at our Guild with the same concerns about the "cold". So, one of our members, made marks and then ironed them. Of course, they disappeared as advertised. She then put the item in the freezer and guess what? All of the marks returned. They also disappeared when ironed.
(A footnote---she had seen them at shows and they were priced but apparently they are available at Office Supply Stores and she even mentioned Wal Greens (haven't checked that out)