Hi Ferg,
They are cutters but can also be used with pens, stylus etc whatever fits in the holder for marking, there is an option in the software for swapping between the knife and a pen. They have a pressure setting so you can determine how dark the tracing is.
Heres a pic of a tracing
Before anyone asks about cutting the knives are tiny so aren't suitable for cutting leather, I did managed to cut 1.5mm thick leather once but definately wouldn't try anything thicker.
The flatbed machine they do would cut through thicker leather but are over $5000 I think, definately not something I could afford they use an air suction system to hold down the piece. My model uses grip wheels to move the mat back and forth and the leather needs to fit between the wheels as they are textured and you wouldn't want them to run over the leather, I use double sided tape to hold the leather to the mat.
Let me know if you would like any other info.
Cheers,
Clair