2.8.21 has a small bug, which can prevent the recoveries from being able to mount the system partition. I have created a patch for use with the creation of pre-rooted flashable packages. You can find it here. You can flash inside a PRFCreator ROM package installation or use the install.bat to install it from windows while in the ROM.
The installer version contains a root exploit. As such, some Anti-Virus programs will trip over the download and deny you access to the file (ESET NOD32 among others). If and when you can not access the file or the zip seems to be corrupted, disable the A/V software for a few minutes and try again!
Unlocked Bootloader users: Stock on UB, CyanogenMod, AOSP and OmniRom
Use the Kernel Builder to repack the kernel you are using now to replace the built in recovery with XZDualRecovery. Installing the locked bootloader variant will either not work at all or require unexpected operating instructions.