It depends upon the OS.

I find that it is reliable for Linux and Windows. It is easy to copy an ISO onto a flash drive, it can store multiple ISOs, and those ISOs can be updated without overwriting other data on the drive. This means application installers and data backups can be stored on the same drive, making it a very convenient recovery drive.

As for other operating systems, they seem to boot partially but the boot process ultimately fails when they try to access the drive directly.