No worries - I fortuitously just installed a bigger SSD on my Mac, so I ended up installing BootCamp and Windows 10, and installing it that way. Everything now up and running!

Thanks - it did seem like it was doing the right things, it's just when I enter 'rkflashtool b' it reboots into a 'switched off' mode, and entering 'adb devices' gives an empty list. Just to give the complete info, I'm running the latest versions fo Homebrew, rkflashtool and Android Platform...

I've been trying this on a Mac and I've come unstuck somewhere along the line. Rkflashtool and ADB both installed fine, but when I try to install boot.img and the TWRP_recovery_.img onto the X5, the flashing process runs, but then I get an extra line in Terminal saying 'premature end-of-file...