You should check out my review on the main game, if you wanna get some more detailed information about this game.
However if you are here for the only the DLC, here is my opinion about it: (I may not have played a lot if you look at my hours, but I have played the mobile version, where the DLC is included in the main game and for free)
The DLC From Outcast to Savior allows you to experience a few more hours of a great story about Sir Gareth's son who became an outcast after Rufus spread the fake news, that Gareth betrayed the Kingdom (I won t spoiler the story).
This DLC also allows you to get access to a few more heroes as well as new units, ballista ammunition types and magic spells that you can use in all game modes.
It is a pretty cool DLC although I would rather recommend you to wait for it to get on sale or buy it from a 3rd party seller or buy the bundle directly from a 3rd party seller for 2-3 keys.