LA is completely fucked and no one who ever worked on it had any clue what they were doing.
Looking at the template in Monsters of Fearun, I wouldn't even give them a Level Adjustement or character level equivalency, I'd let someone play them from 1st level as any normal character, but withhold the psionics until appropriate levels. Say 3rd for poison and 5th for Polymorph, maybe.
If you must give them a LA, I'd say +1 is more than enough, but give them a humanoid hit die for that too.