From what I can see it looks like you use it like a kubotan. You use it to apply pressure to parts of the body or to add weight/stability to your fist.
To be honest if you wanted to kill someone then write a handy note you would be better off with a good fountain pen.
This guy is exactly what I pictured the "cold steel" target demographic to be like.
First off the pen is just too big to comfortably write with, and taking 5-6 turns to get the cap off seems like overkill. I have never had any issue with the cap coming off a regular sharpie, but then agan I never tried to bludgeon someone to death with a sharpie either. That's what maglites are for.