Another thing with static landscapes/meshes from the marketplace is that you can not revise parts of it if you do not like it.
You can alyways go like: yeah, I have to make 7 terrains before I reach the 100bucks for world machine if one terrain taxes in at 15bucks, but the more important part is that if or that bit of the terrain does not fit into your game or you do not like it, then you are stuck with it. Things like that should at least have the world machine file in the package to be able to change that slope or erosion crack and so on.
But then I kind of go with . Creating stuff is really easy and the reasons for not doing it yourself are quite limited. Once the workflow is set, having a terrain like that here in UE4 is done in no-time.