Watched a video about these pens and had to give them a try. I used them today on a small project for the Jeep. My first impression are good and they are about $10 a piece. It’s just pressurized chalk that transfers a highly visible chalk.
This is where these things shine. I was hanging a bracket in my work van today and needed to transfer marks through small holes in a 2x4. The holes were made with a tapered drill bit (1/4” face to 1/16” backside). The marker blasted these points through 1 1/2” thick blocks.