This product is fantastic! At first, I thought it a bit expensive for DM Guild, but I took the gamble anyway, and it was worth it. It is very well polished.
This product is valuable to any DM that is ...
a) Running a Forgetten Realms campaign just before or during the Sundering shenanigans. This is when Shade, the Netherese Shadovar, and Shar was just running amok in Cormyr, Sembia, the Dalelands, and Waterdeep.
b) Running a campaign in the Shadowfell. The Shadowfell is filled with dangers and undead, but also cities and people. These are some of those people.
c) Wants to give players that LOVE THE DARKNESS the thing which they crave, without making them evil or buddies with the undead by default.
I fall under category "a". My players are right in the thick of the plots and machinations of the Princes of Shade just before the Sundering starts happening. They are facing the Empire of Netheril at its most dangerous and this product gives me the tools I need to make that danger very thematic and flavorful. It is also a very accurate adaptation of the abilities that we've grown to love from the Shadovar and their servants from novels by Troy Denning (The Sentinel), Erin M. Evans (Lesser Evils, The Adversary), and Paul S. Kemp (The Erevis Cale Trilogy, The Twilight War Trilogy). This product allows you to bring those shadow-steeped foes to life in your own adventures. Or better yet, allows your players to harness and master the powers of darkness itself!
Now, we could quibble over balance issues and whether some of the archetype abilities are "off-color" for a particular class. But you don't have to. Just like the PHB and DMG, you can use this as a starting point. You can use this product as a collection of darkness-based abilities and creatures that you can mix and match to best suit your taste and the power level of your campaign as a DM. Because each of the archetype's abilities are so unique and so flavorful, you can't go wrong even if you just take one or two and put them where you think they can have the best effect in your story.
For example the "Darkmire" feature is brilliant in its simple elegant design, but utterly terrifying when unleashed by an NPC foe on the party.
So $3 may seem like a lot relative to all the other DM Guild publications, but in this case I believe this product is worth it.