As you may know, Ubuntu Touch is Canonical’s mobile version of the Ubuntu system. While it runs over Unity 8 and Mir, the future generation desktop environment and display server, the Ubuntu desktop still uses X.org and Unity 7.
For now, Ubuntu Touch is available as default only on Bq Aquaris E4.5, Bq Aquaris E5 HD and Meizu MX4, but it is also officially supported on the LG Nexus 4.
At first, the online purchasing of the Meizu MX4 Ubuntu was invitation-only, but after the manufacturer made it available for anyone to order, the phone has been out of stock a few days. But now, the phone is back again.
As a reminder, the Ubuntu Touch OTA-5 Update brought some specific Meizu MX4-optimizations, including battery enhancements.