This was actually a very satisfying excursion set right dab in the middle of the first book of the Warded Man. Right when Arlen is becoming a messenger, out on the field, he gets into some serious demon trouble with none other than the One-Armed Demon, his old nemesis from when he was just a lad. (And the demon remembered his little gift, of course.) 
 Seriously, I keep going back and forth whether I would have loved to see this put BACK into the original novel, despite the length. Kinda like the director's cut. It's perfect there. 
 Sure, it might disrupt the pacing but it sure as hell improves the One-Armed Demon story. And I loved that part of the novel, including the resolution. It's pretty damn heroic. 
 Either way, however, this little novella has plenty else going on and it only improves the general world-building. Nobels, marriage issues, the Messengers, everything. What can I say? I love everything Arlen. Including his youth. :)