There is a difference. Feinting only works against your next melee attack. Two-Weapon Feint does not change that.
However, Improved Two-Weapon Feint says:
If you successfully feint, that opponent is denied his Dexterity bonus to AC until the end of your turn.
Improved Two Weapon Feint increases the duration from your next attack only, to your whole turn (and so all of you attacks can take advantage of that, instead of just your very next one).