I tried dd'ing the ISO image to a pendrive but that didn't work, however reading through the docs (BUILD.md):-Question, can you use mfbsd to create an USB pendrive image ?
## Creating images
You may create three types of output: disc image for use by dd(1),.
ISO image or a simple .tar.gz file
1. disc image
so it looks like you can just by changing the target of the Makefile. I'll give it a try shortly.