Media Creation Tool requires internet access, so you can't just flash a Windows .iso that you have independently downloaded from microsoft.com. Of course, you can always prepare the correct disklabel yourself, use a BOOTSECT.EXE incantation to make the USB bootable, then copy all the files, etc, but this really should be easier than that.
I just tried it and the tool started downloading Windows without giving me an option to select an .iso. It can download .iso's for burning them to DVD's but I don't think it can take dangling .iso's and make installation USBs out of them.
It doesn't support Linux images, though, for reasons that should be obvious.