
Truth: Tharpa Publications does largely sell only Geshe Kelsang's books, but there is nothing wrong with this. For the Kadampa practitioner, these books contain all the teachings required to attain enlightenment, and they form the basis of all NKT study programs.
Each book contains commentary to a root text by Buddha Shakyamuni, Je Tsongkhapa, or another great realized Buddhist master. For example, Ocean of Nectar contains the translation of Chandrakirti's entire root text Guide to the Middle Way, Universal Compassion is a commentary to Geshe Chekhawa's Training the Mind in Seven Points, and Eight Steps to Happiness is a commentary to Geshe Langri Tangpa's Eight Verses of Training the Mind.
Many of the books are structured like Dharma scripture because they are based on the outlines that come from Je Tsongkhapa's texts and they contain a huge number of quotations from Buddhist scriptures and references to other Buddhist texts. In short, they are authentic and authoritative teachings of the Buddha and many other respected Buddhist Masters; they are neither a new creation nor the exclusive work of Geshe Kelsang.

Truth: There is no injunction within the NKT, in the Internal Rules, the NKT books or elsewhere against students reading non-NKT books. Geshe Kelsang's commentaries to Je Tsongkhapa’s teachings form the basis of the three NKT study programmes (the General Programme, Foundation Programme and teacher Training Programme, see Internal Rule 15) but outside of their studies NKT students can and do read what they wish. Everyone has freedom to do as they choose.

Truth: This is not true. There are many students who have been practicing for years with the NKT who have still not taken Heruka and Vajrayogini empowerments.
Taking Highest Yoga Tantra empowerments is an individual decision. Sometimes what pushes people to enter Tantric practice before they have a sufficient understanding of Sutra is a Western mentality of always wanting the highest and the best, rather than the advice of any teacher.
It is true that teachers may explain to their students the benefits of entering the path of Highest Yoga Tantra, but they will likewise explain the conditions under which somebody is ready to enter into the path.
Also, Highest Yoga Tantra empowerments are generally granted only once every two years, not all the time.