Pros:
-Adds quests for the plethora of Minor Factions in the game
-Quests are balanced and give more depth to subdued minor factions
-Quest rewards vary and often include a small army with the minor faction unit.
-Solid plotline for each minor faction.
Cons:
-None
Overall: For $2, you get 20 new quests added to the game that make Minor Factions more of an influential force in the game. Without this, minor factions are fairly two dimensional - subdue them, assimilate the faction with the unit you want, and you're done worrying about them. This gives the option to complete a quest for one of your subdued factions in return for worthwhile rewards, and opens up more possibilties over the course of the game.
Worth it just for the story, which gives some character to the creatures you subdue in your quest for domination. If you own Endless Legend, this is a worthwhile two dollars to spend.
Bottom Line: Recommended