I loved this -- clearly inspired (or tribute) to the beloved Christmas Carol and Chambers is able to write a compelling and convincing story of Quin Flint who realizes that he needs to change the way that he lives his life, without introducing a paranormal element out of it.
The plus point for me is that Chambers doesn't completely change who Quin's is in his core. There's nothing wrong with being single-minded and determined over something you are passionate about -- it can actually do good for others.
The ending is lovely (and again convincing). I can exactly see in my mind's eye how Quin and Rob's relationship is and how Rob fits in Quin's life. They way that Rob keeps Quin on track with his tenacity without going back into the unsympathetic man that readers met at the beginning. So yes, even though the novella pretty much happens in one day, this is where I throw all of my cynicism out the window and believe in the magic of a holiday story.