Criticism: Cmd+left/right/up/down doesn't work - instant dealbreaker.
Getting keyboard navigation reasonably right everywhere will be very difficult. Ironing out the remaining platform differences may be even more difficult.
I also broke it (a nondescript TypeError once, “invariant broken” another time) fairly quickly, by tabbing to the cog thing, Space, tab to the Duplicate button, Space—where clicking didn’t achieve that.