In order to enjoy what DoomLoRD has in store, you would need a model of either one of the two mentioned handsets that come with an unlocked bootloader (stock firmware or ROMs that are based on it), before you perform a flash of a custom kernel. When done, you can then access ClockWorkMod custom recovery (v6.0.4.7). It is from there that you can make the decision as to whether you would like to see the Xperia Z3 or the Xperia Z3 Compact rooted, as you download SuperSU and have it saved onto an SD card while flashing it via CWM.
It is recommended that one downloads BusyBox immediately after the rooting process, before performing an installation in /system/xbin. The list of known issues happen to be rather short at the moment though, which is a good thing – and one that DooMLoRD will fix in due time.