Many thanks @petefoth for your work maintaining the “dev” version of “e” for the Xperia devices. I researched small phones among the devices list available here, and was pleased to discover the Z5 Compact which I thought would be a better replacement for a Samsung A3.
I had installed “e” on the A3 for my partner who hates big modern ones but after an unlucky fall the screen was completely unusable, hence my search for a new e-device.
Following the e-install guide and the Sony help pages I was able to get as far as unlocking the Z5 bootloader, but made the mistake of manually restarting instead of waiting for the long Sony splash screen finish the reboot. The end result was a return to a factory install I suppose as all the text was in ideograms - Japanese I suppose. Not finding a way of changing the language setting I had to navigate through the “getting started” sequence to eventually by trial and error find the developer section to enable USB debugging.
As the last step 6 of “unlocking the bootloader” in the official guide is very succinct on this matter, I found that @mike_from_ireland had written an excellent, very detailed beginner’s guide to install /e/ where he warns about the delayed reboot.
Unfortunately his guide is in the Documentation Suggestions for the Z3 Compact - not quite sure why - but I hope that @Manoj will be able to redirect it here. In fact, I suggest putting a link in the official guide that would point Linux users to this far more detailed set of instructions as @mike_from_ireland explains all the necessary preparatory steps using a Ubuntu distro: a fine job worth a big clap 
So far my partner is very pleased with the Z5 and I was surprised to see how long the battery lasts, having read elsewhere that battery drain had been a problem in the past. As the Z5 has an octa-core Snapdragon CPU it seems a lot “snappier” than the Samsung A3, both phones being about 6 years old now. But the Z5 seems a lot better made.