Not op, but it's not bad but it's definitely not a part of the main three books. You kinda have to consider it like the "jax and the broken house" story. Narrow Road is a bit longer than that story, but it's an order of magnitude less than either of the two 'main' books.

If you like his writing and you're hungry for more of his work, it's a good way to scratch that itch... But it functioned like an appetizer for me, I was sated for a bit but I can tell I'm going to end up even hungrier for the next proper book than I was before.