Cloning an iso file to a mass storage device makes a boot drive, provided it is a hybrid iso file, post-processed with isohybrid. See this link to the isohybrid sub-page.
Also on same link:
mkusb will 'use the whole device', actually only the head end (size of the iso file), but the rest of the device is not available. mkusb simply clones the ISO 9660 file system with its content from the iso file. This ISO 9660 file system works from CD/DVD disks, and also from USB drives. After using a USB pendrive like this, you make a new partition table and file system, if you want to use it for another purpose.
But in wikipedia Hybrid_disc:
A hybrid disc is an optical disc that has multiple file systems installed on it, typically ISO 9660 and HFS+ (or HFS on older discs). One reason for the hybrid format is the restrictions of ISO 9660 (filenames of only eight characters, and a maximum depths of eight directories, similar to the Microsoft FAT file system).
So do I understand it correctly that
isohybrid tool makes ordinary ISO 9660 images, not hybrid ones? What is the meaning of
hybrid apex in
isohybrid, why is it not called something like
isoboot? I could not find that "historic" info via web search.