I have come back on it at around 11:00 and it was quite quiet. Perceptions of safety vary but I have not had any problems returning to FH by train late at night.
Six or seven years ago when I used to go out in the Shoreditch and Hoxton area I would have been so grateful for the Overground. I remember the race down to Old street to get the Northern line back to LB for the last train.....