Less power, more robust, and a lot smaller.
Lenovo ThinkCentre M93: £64.99 I wanted to pick up something used, robust, repairable and extendable. I'd seen a few teardowns of this model and I liked the cooling mechanism: heatsink with a pipe leading to a large slow rpm fan. This replaces my low-power NAS.
Mac mini 2018: £900 This little box has been doing a good service for a while now. Eventually my MacBook will be retired by Apple.