I haven't had the time to go through the OT, but ISTM a number of people have pointed out that it isn't a true LXX translation, and in fact in many places it follows the NKJV rather than the LXX in divergent passages. If that's true, I don't see the point in getting it (the OSB).
The intro to the OSB says that the editors used Alfred Rahlfs edition of the Greek text of the LXX as the basis of the English translation of the OSB. Then, for reference, they used the Brenton translation (1851) of the Greek Old Testament into English. Then they only used the New KJV where the translation of the Masoretic (Hebrew) text and the English translation of the Greek text resulted in the same translation.
So the OSB is significantly different from the NKJV in many places and is a viable translation of the Septuagint. I have found differences in translation between the OSB and NKJV (I have both Bibles).
The OSB uses the same cannonical order of books as does the Old Testament According to the Seventy, first published in 1928 with the approval of the Holy Synod of the Chruch of Greece.
I would guess, that in subsequent editions, like happens with many Bible translations, it will be refined and will come to be a standard LXX English translation for many Orthodox.
I think the people are nitpicking.