One small addition that would make Opus faster to use would be to add a "Sync right-to-left" checkbox under the current "Sync left-to-right". At least one competitor (Powerdesk Pro) has this function. I often sync to a thumb drive and then from the thumb drive to a second computer, then back again. That round trip requires resetting the path for both panes twice per computer. It would be much simpler with a checkbox.
There's a button in the Sync panel next to the paths (and a similar one, optionally, in the file display toolbar which can be used when the Sync panel isn't there) to swap the left and right sides.
Or turn off "left-to-right" and then the sync will always go from whichever side is the source.