I wouldn't say there's "a lot" of non-Orthodox material in there. The development of the Western Rite’s Divine Office began in the very earliest years of the Church’s life after Pentecost, and it developed into its current, essential form by the time of Saints Benedict and Gregory the Great. It is our rich heritage as Orthodox Christians, containing the fulness of the Divine Office as prayed and chanted by our Fathers and Mothers in the faith, having its primitive roots in the worship of the venerable Patriarchs, Prophets, and Apostles, being given its distinctive form and content by the holy Fathers, Martyrs and Confessors of the Orthodox Western Churches. It is the Faith of our Fathers, expressed according to the particular genius of the Western Latin mindset, in the traditional English idiom of prayer and worship that so many hold dear.
The only caution needed is that it might ignite a fire in your soul that so many of your Western forbears had during the first millennium of Church history, and it might make you want to experience more of the venerable Western Rite