All of the activities in DoReMi Piano are beneficial to students of any instrument. They are based on the Kodály Approach, used internationally to teach musicianship to pre-instrumentalists. In the United Kingdom, where Kodály is not commonly used in primary schools, many instrumental teachers use the approach with their students.
If you would like to learn more about this approach to music education then I would advise contacting the British Kodály Academy. They run excellent courses for musicians and music teachers. See their website at http://kodaly.org.uk