Fr Griffiths book was created for the use of the Catholic community of Kurushimala Asharam, when they decided to use the Malankara rite in their worship.
Fr Griffiths did approach HH Mathews I Catholicos of the Malankara Orthodox Church for an imprimatur to be granted for the use of this book in Malankara Orthodox worship. If I am not wrong the same was granted.
In English this is the best book available and I guess it is the only one available as well. I own a copy as well, go for it.