My larger concerns about belaying in the hills are:
That the theory of only employing a dynamic belay in the mountains, as told to me by books and friends, would be prone to human error when you are tired. That is it might work when you are fully awake and at the start of a climb but 20 hours into an ascent the idea that you would be awake enough to only let some rope slip through your belay device before applying friction seems false.
It sounds like it is better to hold the belay device in a locked position.
Marty