Which one is more useful if you are using it for a secondary device? The thing about pencil is that it distincts the iPad and Macbook meanwhile the keyboard would provide a pretty similar Macbook experience. Idk if the 9.7" or 10.5" would have a screen big enough for you to write or take notes using the pencil? Perhaps pencil for the 12.9" and keyboard for the 9.7" iPP? Which would help you more?