How is it superior to a straight-classed Psion or PsyWar, though?
Illithid feats are considered "Psionic" feats, so they're counted under the Psion/PsyWar bonus feat lists. You get 4 of these Illithid feats as bonus feats; in exchange, you give up 4 ML.
So, for a PsyWar, it's straight up a bad trade. You lose BAB and ML, while the only thing you gain in return is a better Mind Blast that can be used 6 times a day. A PsyWar 20 would effectively have the same number of bonus feats as a PsyWar 10/FP 10, but would be able to choose them more freely.
For a Psion, then... Are two bonus feats, a slightly bigger hit die, and an improved Mind Blast worth 4 ML? I suppose it could be a matter of opinion. I'm not sure if it's ever a particularly good tradeoff, but YMMV.
Also, how on earth did you take Illithid Savant?
Flayerspawn Psychic does not turn you into a Mind Flayer...