The 2009 revision that you mentioned is limited in scope (in terms of who uses it). Here is a summary of it from
Wikipedia:
In 2009, on the occasion of the Synod of African Bishops in Rome, the Catholic Church in Africa published a new English edition of the Liturgy of the Hours based on the Liturgia Horarum, editio typica altera. The antiphons and orations in this edition are taken from ICEL’s 1975 translation of the Liturgy of the Hours, with independent translations for the offices for the new saints added to the General Roman Calendar as well as the Benedictus and Magnificat antiphons for the 3 year cycle on Sundays added in the Liturgia Horarum, editio typica altera. The Psalms are taken from the Revised Grail Psalter with the rest of the biblical texts taken from the New American Bible. To-date, this is the only official English edition of the Office that is based on the Liturgia Horarum, editio typica altera.
So unless you are in one of these African dioceses, it would probably be better for you not to get a breviary which was published in accord with the 2009 revision.
On the other hand, here is Wikipedia’s summary of the 1975 edition:
The Liturgy of the Hours, produced by the International Commission on English in the Liturgy (ICEL), was first published in 1975 by Catholic Book Publishing Company in the USA. This edition is the official English edition for use in the USA, Canada and some other English-speaking dioceses. It is in four volumes, an arrangement identical to the original Latin typical edition.
So, to answer your question, the 1975 edition is not only still approved, but it is still the official edition and translation for many English-speaking countries.
