What are the mkusb options "msdos", "upefi" and "d-n-i"?

I'm trying to create a persistent live Ubuntu bootable USB drive using mkusb.

In the "Persistent live drive settings" I have the options "msdos", "upefi" and "d-n-i", and also have the buttons "Use defaults" and "OK".

Unfortunately, I couldn't find in the wiki nor the manual what each item or the "Use defaults" button does.

Clicking "Use defaults" is the same as clicking "OK" without any item selected? And what is the meaning of each item? When should (or shouldn't) each one be used?

You can select

• MSDOS partition table (while default is GUID partition table, GPT). This can help in some HP computers, that are unwilling to boot with grub and GPT.

• UPEFI, 'usb-pack-efi' (while default is to use the grub system from the iso file). The 'usb-pack-efi' grub system works in UEFI and BIOS mode. It was developed from a multiboot system for UEFI by Andre Rodovalho. See this link and links from it.

• D-N-I, download and install security updates (while default is to display a message when there are security updates). The default option was created for the early versions of 16.04.x LTS in order to avoid overfilling the casper-rw file system, if too small for substantial upgrades. See this link for more details.

• Clicking "Use defaults" is the same as clicking "OK" without any item selected.