NextDayMobiles did deliver the next day.
So I have it and have done the install already.
I had a problem connecting the device before flashing and that was down to not knowing that I had to set the USB preferences to file transfer.
I had to use fastboot flashing unlock to unlock the bootloader.
I could not get the online Android flash tool to work at all after I had managed to set the device to developer mode and unlocked the bootloader.
So I just ran the ./flash-all.sh provided with the Android 9 image.
I used the app image of the UBPorts installer.
I had a little trouble getting the UBPorts installer to recognise the device but it worked after closing it and re-opening it.

Looking forwards to using it in earnest.
What's the best next steps?

channel 20.04 stable.
Seems to be working OK.
I don't use the phone much but I can make and receive calls on my pay as you go Three UK sim fine.
One of the reasons for doing this was to be able to hear incoming calls better, it could just be me, or maybe the caller that I could hardly make out, but it seems loud enough in testing.

And I got my custom ringtones and notification audio clips installed without faffing about with copying files which I had to do originally, so that is better now.