My wife and myself are Secular Order Discalced Carmelites, and we are required to say the morning and evening prayer, from the breviary. For years, we used the single version, “Christian Prayer, The Liturgy of the Hours.” We didn’t get the four volume set, because two copies of it would run almost $300. However, last year we managed to get one set free, and another for $120, so we now both have the 4 Volume sets.
My advice to the OP, and anyone else is, the single volume Christian Prayer, The Liturgy of the Hours, is complete for morning and evening prayer. You can use it in a group, even with people who have the four volume set. Most people only have time for morning and eveing prayer, and perhaps night prayer, and the single volume is all they will ever need.
However, if pride or your desire to do the Office of the Readings is really strong and you have the cash, go ahead and get the four volume set.
Myself, I’ve only done the Office of the Readings twice in the past year, and it wasn’t really necessary to get the four volume set.
Also, the single volume is easier to use. Don’t think that you won’t have to flip back and forth in the four volume set, because you do.
And last but not least, the single volume has the actual music, not just the words, to the hymns. The four volume set has only the words. However, I never sing the hymns when praying alone anyway, so its a non-issue for me.
Jim