Much more flexible
the USB Multiboot creator can work to some extent, this device is another step up..
I hold all my dev tool ISO images as well as OS install ISO's, the only limit is the size of HDD you fit in..
I've also run into some linunx live-cd's that have been poorly created such that they expect the files to be on a CD drive, something the USB creator doesn't fully emulate in the same hardware way.
Plus, having the dual mode is handy, all my drivers/support files are also available while the image is mounted, making it that little bit more flexible..