Awesome work! I upgraded my Meizu Pro 5.
Noting my success details posted at https://forums.ubports.com/post/14164
I had Meizu Pro 5 Ubuntu Edition but run into the https://forums.ubports.com/assets/uploads/files/1528013524195-8a15d567-ca4b-44ca-a1ce-84fdb7e0aec7-image.png screen when first trying to update it to Ubports 16.04/stable channel.
Somehow now later I managed to flash - with ubuntu-device-flash - from within 16.04 ubuntu installation (actually, 16.04 lxd container with usb vendor specific passthrough). I did that by booting to Ubuntu's recovery installation with power button + volume up - this is where you might need the recovery-turbo.img but I had it flashed already.
I verified that from within my lxc container (where I had added lxc config device add CONTAINERNAME meizu usb vendorid=18d1) I was able to see the device with 'adb devices'. Then I ran ubuntu-device-flash --server=http://system-image.ubports.com touch --device=turbo --channel=ubports-touch/15.04/stable - I thought it got stuck after downloads, but actually then it started the "Pushing" phase. And even more to my surprise, it rebooted to flashing phase with Ubuntu prorgress bar going back and forth, and then booted into working Ubports installation! Even though I specified "15.04/stable", it seems it too pointed to 16.04 already, ie OTA-5.
The greatest thing was that since I didn't need to specify --bootstrap or --wipe, it was even the same installation I used as my main phone back in the days, so I had all my apps and photos intact.