Usage is quite basic, just do File->Import->Speedtree Material(.stmat)
choose a .stmat file and the materials will be automatically created and all textures loaded and linked.
Workflow is now as simple as import a mesh, import the corresponding .stmat file, add a light and a camera, Render !

In the material panel, you'll find an option to add thickness to each material because subsurface scattering works well on thin object than just planes ! This can be done automatically at import time for all materials flagged double sided in speedtree and that use subsurface scattering, this ensure a better rendering of leafs or petals for example. Just tick the "Auto thickness" checkbox in the import options.