I used the single volume, "Christian Prayer, The Liturgy of the Hours, for about 12 years. Last year, my wife and myself purchased the 4 volume set.
I found that for most people, the Christian Prayer version will fit them the best. It has Morning and Evening Prayer, just as the 4 volume set, and its what most people are limited to with their work schedules. Its also simpler to follow.
The 4 volume set, has the complete Office of the Reading, which is usually said at vigils, before morning prayer. However, for must of us, praying the OR before we leave to work is longer than we have time for, and if you’re like myself being half asleep at that time, its more difficult to get through. So, I skip the OR and do the Morning Prayer, which I did with the single volume “Christian Prayer.”
In my former OCDS group, we advised the new members to begin with Christian Prayer, which the majority of members had. Most of the 3rd order groups or parish groups who pray the LOH, will do morning or evening prayer, not the OR. So, the Christian Prayer version is actually the more suitable for most lay people, in my opinion.
You can probably purchase either versions, used, at
Amazon.com
Jim