I have an M3 hub although I haven't played with it extensively. It paired to Hubitat as a 'bridge'.
The way Aqara have implemented this is that any device within M3 e.g. ZigBee seems to be accessible via HE however any devices paired to the M3 bridge via Matter do not get onwardly exposed from M3 to HE which is what I had hoped and yourself I think. I suspect Aqara reason this can already be achieved directly in Matter already although they don't provide a 'share' function themselves to assist within M3. My Hue system gets into M3 via Matter but does not propagate onto HE this way for example although there are other better ways for this anyway
There are currently very few devices that will pair over Matter to the M3 but after poor feedback from users Aqara have just announced they are expanding this significantly so it should get better. Aqara are responding quickly on Reddit with OTA updates as users are raising issues.
