Short answer: upgrade for a missing role, not for the model number
M3 is the better foundation for a new Aqara-centered system that needs Thread, third-party Matter control in Aqara Home, Matter bridging, PoE, or edge-hub features. M2 remains the lower-friction choice when it already runs stable Zigbee automations and none of those new roles solves a documented problem.
M3 adds Thread and a broader Matter-controller role
M3 can act as a Thread border router, commission supported third-party Matter devices into Aqara Home, and bridge supported Aqara devices to other Matter controllers. M2 is primarily a Zigbee 3.0 hub with Ethernet, infrared control, and ecosystem bridging for compatible devices.
PoE can change where the hub lives
M3 accepts compatible PoE, so one Ethernet run can provide network and power at a central wall, ceiling, or equipment location. M2 has Ethernet but uses separate Micro-USB power. PoE adds value only when the switch, injector, cable path, and mounting location are already planned.
M2 can remain beside M3 during migration
Aqara describes M3 as an edge hub that can coordinate an Aqara hub cluster, but that does not eliminate migration work. Keeping M2 active while a small set of devices and automations is verified gives the household a rollback path and avoids resetting a stable installation in one session.
Matter bridging does not expose every feature
A bridged Zigbee device remains Zigbee, and the destination ecosystem receives only the functions represented by Aqara's bridge and its own Matter implementation. Advanced Aqara settings, infrared scenes, vendor-specific data, and some automations can remain available only in Aqara Home.
Home Assistant does not make M3 automatically unnecessary
Home Assistant can run its own Matter controller and Thread border router, while M3 can bridge supported Aqara devices into Home Assistant. The useful question is whether Aqara Home automations, Zigbee migration, PoE, infrared control, or Aqara Thread devices justify keeping M3 in that architecture.
Price the accessories and migration time
Compare the current M3 price with any required PoE switch or injector, USB power adapter, Ethernet run, and the time needed to rebuild or verify automations. A discounted M3 is not a saving when the existing M2 already covers every real use case.
Choose M3 when
Choose M3 for a new Aqara-heavy installation, planned Aqara Thread devices, supported third-party Matter devices inside Aqara Home, PoE placement, or a deliberate Matter-bridge path into Apple Home, Google Home, SmartThings, Alexa, or Home Assistant.
Keep M2 when
Keep M2 when its Zigbee automations are stable, Ethernet and infrared already solve the routine, another controller handles Matter and Thread, and no current device requires M3. Revisit the decision when a specific new device or automation creates a missing role.