I am very pleased with the Mac mini itself and feel it represents excellent value for money. The only challenge was the initial setup. The machine arrived with a previously installed system, but without the password, which meant I had to erase the drive and reinstall macOS from scratch before I could use it.
As someone reasonably comfortable with technology, I eventually worked through the process, but it took a fair amount of research and trial and error. I wonder whether it would be helpful for Back Market to include a short setup guide for situations like this, covering a few simple steps such as:
What to do if a login password is unknown.
How to start in Recovery Mode.
How to erase the drive and reinstall macOS.
The importance of having a wired USB keyboard available, as Bluetooth devices may not work during initial setup.
This is intended as constructive feedback rather than criticism. Once I got through the setup process, the Mac mini worked perfectly and I am very happy with my purchase.