Shelly 1PM Gen4 vs Shelly i4 Gen3

The Shelly 1PM Gen4 wins overall by a wide margin. It has a 16A relay, energy monitoring, dry and wet contact modes, and Wi-Fi, Bluetooth, Zigbee and Matter connectivity with HomeKit and SmartThings support. The Shelly i4 Gen3 is cheaper but has no relay output at all.

The 1PM Gen4 acts, the i4 listens. The Shelly 1PM Gen4 switches and measures a circuit and can even work as a Zigbee router. The Shelly i4 Gen3 has four inputs, no relay and no metering, so it exists to trigger scenes from switches you already have on the wall.

Wi-Fi on 2.4GHz, Bluetooth, Zigbee (with a Zigbee hub) and Matter, plus integration with Alexa, Google Home, Apple HomeKit, SmartThings and Home Assistant, including Zigbee2MQTT. In Zigbee mode it also repeats the mesh. The Shelly i4 Gen3 is Wi-Fi and Bluetooth only, with Matter but no Zigbee.

On mains power, yes: it needs a neutral on 110-240V AC and only runs without one from a 12-48V DC supply. The Shelly i4 Gen3 needs one too: it is powered from 110-240V AC through its L and N terminals, even though it only reads inputs rather than powering a load.

Buy the Shelly 1PM Gen4 if you want one module that switches a 16A load, reports its consumption, runs from AC or DC, and can run on Wi-Fi or Zigbee with Matter and HomeKit support. It is the most flexible single-channel relay in the Shelly range.

Buy the Shelly i4 Gen3 if you want to keep your existing wall switches or wire dry-contact buttons and sensors into scenes and automations. It is cheap, fast and compact, works as a Bluetooth gateway, and pairs naturally with relay modules that do the actual switching.