izigame.me

In short, this DLC presents an in-game avenue to track down various hidden treasures rather than using a wiki or other resource. There's some light puzzle-solving elements to the various treasure maps, which can be fun depending on your preference for that sort of thing.
The only annoyance was that some of the remote treasures involved high-skill locks, which I had to come back to later. There's not really a great way to track which treasures you've found in-game (the maps tell you whether you've read them or not, but not whether you've gotten the respective treasure).
I found the Warhorse armor to be a nice alternative set of armor, as it has higher stats (though not the best in the game) and is strong even into late game. It also has a very low value, which makes paying for repairs extremely cheap compared to similar armors (which also means it takes less of an armorsmith's kit to repair).
I'm not sure if I'd buy it as a separate DLC, but I'd recommend it when bundled with the base game. For what it's worth, I tracked which treasures I still needed and kept an eye out for unread maps in the game. Based on that, I'd recommend giving it a try as part of your KCD playthrough.