This new stuff called "Spray Klaf." The claim was that it was Mei Klaf in spray form. I have been using Mei Klaf(usually with an Eida Chareidit Hekhsher) for years. I have never seen Mei Klaf do this. The letters litterally are not davuk to the klaf. I can erase them with a rubber eraser, and break them by running my fingernail over them. Here is a picture of a Mezzuzah that I wrote with "Spray Klaf" treated Klaf. The damage done occurred from simply rolling the Mezzuzah.