| Neostrider |
The key difference is the barrier to learning, and the scope of the benefit.
Two Weapon Feint is a neat way of giving a character that uses two weapons to feint during a full attack, which is much better than as a move action once the character gets BAB +6/1. He still gets to make two attack in a turn that he has feinted.
But feinting lasts until your next attack.
Improved Two weapon feint has a much larger barrier to learn, but the benefit is that the target loses their dexterity until the end of the user's turn. Suddenly all attacks made become easier to hit and possibly dealing sneak attack damage as well.
So the question is should one be a prereq of the other. My impression is no, because the differences between the feats are relatively minor compared to what another feat could get a character at level 6 or higher. What the two feats provides us is two different ways characters could access a similar ability. Ones easy to achieve, the other has a more powerful effect (but not so much more powerful that it would require two feats to learn)