If the author is reading this: please link back to the introduction / part 1 where you explain the overall premise, not just to part 4.
https://blog.jmdawson.co.uk/i-bought-200-raspberry-pi-model-...
https://blog.jmdawson.co.uk/i-bought-200-raspberry-pi-model-...
https://blog.jmdawson.co.uk/i-bought-200-raspberry-pi-model-...
https://blog.jmdawson.co.uk/i-bought-200-raspberry-pi-model-...