Vajrayana Buddhism runs a strict distinction between mantras anyone may recite and mantras that come only with the empowerment authorising the practice they belong to. This one is emphatically in the first class, and its openness is not an accident of publication.
It is carved into stone at roadsides and on mani walls, printed in blocks and hung as prayer flags, rolled into cylinders and turned, painted on rock faces, and taught to children. Tibetan teachers state without qualification that no permission is needed. Its association with Avalokiteshvara, and through him with the Dalai Lamas as his emanation, made it in effect the national formula of Tibet, and its recitation has functioned since 1959 as a marker of Tibetan identity under Chinese rule.
The contrast with the closed material is deliberate on the tradition's part rather than accidental. The mantras of specific meditational deities, the practices of the higher tantras, and the hundred-syllable purification formula are transmitted inside the rite that confers them, together with the visualisations they are inseparable from, and are not published for general use. This collection records that distinction and supplies nothing from the closed side of it.
The commonest Western error is to reason from the availability of this one to the availability of all of them, and then to treat a teacher's refusal as secrecy for its own sake. The tradition's own reasoning is that a mantra without its practice and its transmission is a sound without a technique, and that supplying the first without the second is not generosity.