It’s compatible with any mesh, although it depends on whether the mesh is static or skeletal. The full price version can do both, while the free version I’m pretty sure only does skeletal meshes. It’s easy enough to convert a static mesh to a skeletal mesh though so you could google tutorials on how to do that.
In regards to performance, it really depends. The plugin works based on shell texturing, which duplicates the mesh and offsets it outwards for as many layers as you specify. The more layers, the more realistic the fibers look. For example, a mesh with 1000 triangles with 10 layers will be rendered like a 10,000 triangle mesh. If the numbers get too high, you can use LODs to easily lower the layer number the further the camera is from the mesh.
I’ve never used this plugin for anything other than characters. You could definitely use it for a landscape, but I’m not sure what the best way to optimize it would be as it takes up a big portion of the level. Probably could break the landscape up into smaller chunks and play around with each chunk’s LODs until you like the final look of it!