I was leaning toward this gem until I considered that I’d rather pray with the whole Church than with the Benedictines alone. Still, it looks good enough to justify taking a 3rd order on its merits alone!
You would still be praying with the whole Church. The Benedictine breviary (current) has the same collects and intercessions as the LOTH. The basic structure is the same. The same canticles (OT, NT, and Gospel) are prayed every day, and the GILH says that it fulfills the obligation of those under obedience to pray the LOTH.
The only difference is the psalter: Benedictines praying either Schema A or B pray the entire psalter in a week (schema A is in a week and then some in fact as many psalms are repeated, such as 3, 4, 50, 66, 90, 94 and 133 every day plus the Gradual psalms at the minor hours on Tuesday through Saturday); other schemas do it in 2 weeks. So the psalm placement and order are somewhat different.
Still there is some overlap, such as Sunday Vespers, Sunday Compline, parts of Lauds, Friday Lauds (psalm 50 is used every day at Lauds in the Benedictine breviary, and every Friday in the Roman LOTH).
There are some differences in the calendar; some Benedictine saints not in the General Roman Calendar; some feasts raised from memorials to feasts or solemnities for Benedictine saints (including St. Benedict, and St. Scholastica), and some saints in the general calendar are reduced to optional memorials or not observed at all. But overall there is much more in common between the two calendars, than there are differences.
On the other hand, using a non-official early breviary, or using the 1962 breviary but praying it in the vernacular, would
not be liturgical prayer and would thus not be praying with the entire Church.