I'm a refugee from UniFi and have been setting up a new Omada network at home, with a remote site at the in-law's managed by the same controller. So far so good... there are a few things that could be better, but overall I'm pleased. One issue that I think will be a problem sooner than later is the following.

I'm attempting to pre-configure the WAN for the PPPoE ISP at the inlaw's. I'm a little concerned about what happens if I get the PPPoE setup wrong and they try to set things up when they get home.

It appears that if the ER605 can't connect to a controller, you can do a factory reset, and then configure the WAN correctly. If you also add the controller's FQDN or IP, it will appear as pending on the controller again, and can be adopted. But at that point, I have to manually reconfigure everything else. The networks appear to be reconfigured correctly on adoption, but the VPN configuration disappears. Not the end of the world, but annoying.

Restoring a backup will work, but that will overwrite the WAN configuration and you're back to square one. Backup files don't appear to be human readable/editable, so patching the backup is out.

Any other suggestions would be appreciated... I have a feeling this is not going to be the smoothest of deployments.