Yes, that's the one. Unfortunately around the time of the introduction of the Android 5 update on that handset, they also locked down the bootloader. As far as I'm aware (and a quick search of the XDA forums), it seems that it will probably never be unlocked. Such a shame because it is a great phone being left behind.
It worries me that the unlocking of many phones relies on manufacturer websites that might not be there one day. Hell, even the Xiaomi Mi4c required unlocking with "identity verification" via SMS.
