Hey!
The way STM currently works, I believe it batches materials for each individual mesh at the moment. It creates a new material using the "material" variable as a base because each font will need a new material. But at the moment, these generated materials are only shared between the mesh they exist on, not all meshes in the scene. I'll see what I can do about this, as this would be a pretty good performance boost for a scene with multiple materials.
That said... I've had customers ship mobile games and never tell me about performance issues, period? So I don't think performance will be affected, but I'll still see if I can do anything to batch materials per-scene instead of per-mesh.
The next patch going up already cleans up GC to practically be gone, so that's already a big performance boost, if any!
Edit: also, this might be caused by shader passes, and I'm having my shaders optimized for a future patch... I'll let you know if that fixes this!