Two comments. (Yes I know this was a finished PrC that's being reposted after it got lost on the WoTC board): First:

Though all adepts have tremendous mental focus, a Master sees the entirety of combat as just another exercise of concentration. A Master of Diamond Mind no longer automatically fails attack rolls on a natural 1, nor automatically succeeds on a natural 20.
I don't really see the point of the second bit and this is the only one of the 9 that gets a drawback.

Masters of One are particular enemies of Masters of Nine, and most will attack a Master of Nine on sight.
This seems to presume a high degree of violence and a general lack of ethical tendencies. Maybe just move them generally 1 step closer to hostile?