I recently moved from deConz to Zigbee2MQTT, which I have all setup and working properly. I rebooted my Pi, and after the reboot HA discovered (in the Integrations) the Sonoff Zigbee 3.0 USB Dongle Plus. Underneath the Sonoff line it says “Zigbee Home Automation” and then it has a CONFIGURE button.
Call me crazy, but I already have the Sonoff configured through the Zigbee2MQTT Add On.
So my question is: Should I ignore this, or configure it?
Ignore it
If you configure it you’ll configure ZHA, and it and Z2M will fight it out over your coordinator, breaking everything.
This would be a Bad Thing 
Thank you for the confirmation on my suspicion.
Call me crazy… but maybe it shouldn’t do that.
The devs were talking about it a while back, since they recognised that it’s a bad idea and a common cause of broken installs, but I don’t know if it went further than we really should fix that.
THANK YOU this saved me from a near-disaster.
Part of me was – I want everything configured as HA is requesting, it should go through that workflow since HA knows best.
And part of me was – this seems fishy, I just finished installing Z2M, something bad will happen.
So glad I googled.
This really SHOULD be fixed especially for newbies like me who just got into HA supe recently.