Can't help but get in on this thread.
The EdgeOS UI is SO SLOW. Applying changes is slow. It's incomplete.
Not having a 'test' option for applying changes in the UI, painful. (It's in the CLI)
Not having a batch apply for configuration in the UI, makes some things impossible (It's in the CLI)
I run into this because I use a lot of ER-X-SFP units and I put all the interfaces in a switch. Have to drop to CLI to remove the IP from eth0, add all interfaces to the switch, and add IP to the switch. Then confirm it and it works. In the UI, no real way to do this. Same is true of an EP-R6.