I have been working on getting displacements to work with landscape actors and i have finally achieved a good result.
The below showcases a landscape actor with 2 materials blended both with tessellated displacement and tessellation LOD. I created all of the assets accept for the particle effects, i also have some volumetrics going on to give it some cold air fog.
I am still going to go through and detail it out with foliage etc.
Watch i HD
https://youtube.com/watch?v=4Mq9B4rjlG8
That has a lot of detail to it. You must have a very complex material. Would you mind sharing some screenshots? I would love to see how you did this. 
It is beyond me to why we are required to pay for something like when it should be included in the UE4 Editor, as you can Displace practically every other type of object/actor. I don’t understand why the Developers at UE4 haven’t included as you can Displace almost everything BUT Landscape in the editor. I don’t know how much work was needed to make this “addon”, but honestly when you restrict the displacement to everything BUT Landscapes, you are hindering the ability of developers and prevent great visual works from being made.
I think (personally) that either should be added in/fixed in UE4 or the maker of this “addon” should drop the price to something like $5 as that seems like a more appropriate price compared to what it is now (that being $15). I would understand it you made a bunch of materials from scratch and charged $15, but when (from what is looks like) you use everything that is already in-engine that should not be costing the steep about that is being asked. In fact, since everything is already in-engine how is allowed? What I mean is, how is the person who made allowed to make money off of something that is being done in the editor? That seems a bit odd to me as he isn’t really “Making” anything from scratch, and instead (again from what I can tell) just adding in nodes and changing some values.
Now I could be wrong on this, but there isn’t a lot of screenshots of what is going on in the background. So I am just going on what I can visually see for myself.
I agree that functionality should work out of the box in UE4 the same as any other tessellated material setup but since it currently does not i had to spend quite a bit of time creating and testing a parametrized material node tree to get to work correctly which is why i am charging for it.
It’s actually worth much more than $15 and would cost much, much more if you were to contract someone to build it for you.
The other option would be to invest your time in taking the hours, days, weeks, months or even years it takes to learn the process of creating the assets people put on the marketplace.