Hey! I should probably make this more clear in the docs - you have to make a new material for the new mesh to allow them to have different shader settings. This lets material settings be stored in a material, rather than in the STM component, so setting can be shared between text meshes, but you do need to make a new material to do otherwise w/ it.
I can't seem to recreate the second issue you mention - I'm creating a new gameobject under a canvas, attaching STM as a component to it, and it seems to be showing up fine? Could you give me more details?