PC EFI is a technology to run Mac OS X on any pc with close to macs specs, without any modifications to osx kernel.
Is it legal ?
Yes, it’s legal to have this files, because it’s built from sources apple provided, before apsl2 was changed a year ago.
How it can be used?
It can be used in two ways - installing to hfs partition using startupfiletool and using grub to boot bootloader.
What else I need to run OSX on my pc ?
You need a legal copy of MacOSX (you can buy it at apple.com) and small kext to emulate apple’s “tpm”(which is actualy smc device).
What a difference between diskXsX and rdiskXsX?
diskXsX is a disk device which can be mounted, but when it mounter, it can’t be accessed
(about root partition) , rdiskXsX cab be accessed any time, for read or write operations.
U also can read technical faq for pc efi here.