Honestly I'd just move omni-proficiency to lv1, and have Exotic Weapon Proficiency as a class prereq in place of Improved Disarm; that way you're not increasing the power of weapons you can use.
Originally Posted by The-Mage-King
But... That allows for a brief dip, and doesn't encourage sticking with the class...
"You have a weapon you could have bought anyway" doesn't amount to much. True, it's hard to disarm you, but that just makes it equivalent to a soulknife. The most useful parts of the ability are that it applies to both weapons when dual-wielding, and makes Dex-based melee fighters better if they need to switch to a ranged weapon.
There is more than enough room here to slap on some abilities related to hiding your identity at higher levels. Since your weapon's power is supposed to be relative to your character level, granting a weapon that scales with your class level means that your class features become weaker whenever you take a level that's not in this class, including after you've completed the PrC.