Quoted:
So it's bettter than a LOC from your CO, but not better than a LOC from a flag officer right? From my days in the Navy, I remember a Flag LOC being worth 1 point towards advancement, and a NAM being worth 2. Is it the same in the USMC?
no, promotions in the Marine Corps usually go off a cutting score to pick up corporal or sergeant. As I understand it, this score to pick up is dictated by HQMC on the needs of the Marine Corps and how many Marines a specific MOS needs at a certain rank. So the score to pick up corporal in a one MOS will be completely different from the score for another MOS.
A Marines individual score is computed off of several things, such as PFT/CFT, rifle range score, pros/cons, time in grade/service, MCIs, and Im sure Im missing something else. When your individual score meets the score HQMC puts out for the month, you get promoted. The process then changes for sergeant and higher.