While these moves do kind of the same thing (get someone else to do what you want them to do), they accomplish it by different methods and in different contexts. In the case of direct-brain whisper projection, you are putting the immediate whammy on someone. You make eye-contact and kapow! The effect is immediate, and is therefore limited to the immediate context; "Drop the weapon," or "Let the girl go," or "Give me the Loc-Nar." Further, the coercive nature of this move is also immediate. Once the person is out of your presence, there's no guarantee that they'll continue to do what you want them to do (just like any other use of go agro[/I] once the threat of immediate physical violence has passed).
In the case of in-brain puppet strings, however, you are planting a seed for future payoff. The phrase "no matter the circumstances" is important here. Time, distance, you name it - once that command has been planted, you have leverage over someone - they either do what you want (and thus discharge the hold), or you have carte blanche to mess with them (potentially lethally, in the case of NPCs). You don't have to be in their presence and the effect doesn't "expire." But the trick here is that the NPC is under no compunction to perform that command immediately, nor does the presence of that command prevent the NPC from otherwise acting counter to your interests (knowingly or unknowingly). Unlike the immediacy of go aggro (which is an attention-consuming, direct physical threat), the payoff for in-brain puppet strings is definitely best used "down the road."
Additionally, even with a violation glove, you'd still need to touch someone in order to pull off the latter move. With direct-brain whisper projection, they just need to be able to see you. That's a hell of a lot easier to pull off, and is useful in a much wider array of situations.