There are huge differences between the Monastic and Roman Breviary.
For one, the Roman Breviary recites far fewer psalms in a week, 150 vs about 250 in the Monastic Office (if doing Matins). Matins in the Monastic Office is two nocturnes of 6 psalms. The Roman Breviary has 9 psalms.
In the Monastic Office, Compline is Ps. 4, 90 and 133 every day; in the Roman those psalms are on Sunday only, different psalms are used during the week. In the monastic office, the responsory “in manus tuas” and the gospel canticle Nunc Dimittis (canticle of Symeon) are not said (though since Vatican II some monasteries now include them). Compline was intended to be recited from memory in the dark.
Lauds is different: in the Monastic Office, every day Lauds starts with Ps. 66 in directum, and 50 (with antiphon) and ends with 148-149-150 under one antiphon.
The minor hours are different; in the Monastic, for Terce, Sext and None of Saturday and Monday it’s the different sections of Ps. 118; the rest of the week, it’s invariably the gradual psalms every day (119-127). The reason: they were easy to memorize and so when monks were working in the fields and couldn’t get back to the oratory for the minor hours, they could recite them from memory in the fields. Prime is also different.
Vespers is 5 psalms in the Roman, 4 in the Monastic; in the Roman it includes the gradual psalms plus the same series as Vespers of the Monastic Office. Vespers will be the office in the Roman that most resembles the monastic.
The antiphons will be different because of the practice of dividing the psalms into equal sections, in the Roman Office, that required creating a new series of antiphons.
Finally, the calendars will be different. The Benedictines have their own calendar.
The monastic office is a big challenge. It was never designed for use by the laity in secular life. There are some lighter post-Vatican II schemas (our abbey uses a 150 psalm per week schema and there are a couple of 2-week schemas). But it is more traditional: it’s 1500 years old, whereas the Roman Breviary is only 113 years old. Both are meant to be prayed in Latin only. The English translation of the MD is not liturgical, AFAIK.
Here is the psalm schema for the
Monastic Breviary
Here is the psalm scheme for the
Roman Breviary
In reality the Roman Breviary resembles the current LOTH a bit more than the Monastic Breviary.
Honestly, my advice is that if you regularly attend an OF Mass then use the current LOTH or one of the current post-Vatican II monastic versions (the traditional Monastic schema still exists largely unchanged in psalm layout except for redistribution of the psalms of Prime, in post-conciliar form). But the LOTH is far more manageable, and if you dig beneath the surface, there are a lot of monastic traditions or options that have been retained.
If you regularly attend an EF Mass, then use a pre-conciliar version in Latin.
The Liturgy is meant to be an organic whole with the Mass as its summit, so praying a pre-conciliar office like the MD or Roman Breviary with the OF Mass would be incongruent as would using a post-conciliar office with the EF Mass. For example the gospel canticle antiphons for the proper of the seasons is anchored to the Mass gospel reading, which is obviously going to be different EF vs OF.
I use the 4-volume LOTH chanted in Latin, daily. When I have a bit more time I use the monastic schema of the abbey I’m affiliated with.
