The biggest difference I can see is that CttS has the handicap of preventing whoever is using it (it is also possible to get it from a Psi-Implant on page 153) cannot feel/sense evil/magic/supernatural nor receive telepathic messages. It mentions 'reached by empathy' but I'm not sure what that means unless it refers to Empathic Transmission which seems like a good thing not to be open to... unless maybe it is a creature that communicates with feelings, like picking up on the emotions of someone with an open Third Eye.
In exchange for that downside, does CttS have any advantages over Null Void? I am trying to figure out if it protects against something which Psi-Nullifiers are not protected against. It mentions a list of named powers:
- See Aura
Sense Magic
Detect Psionics
Clairvoyance
Remote Viewing
NV gives an explicit (though paraphrased) list too, but it is not identical:
- Presence Sense ("sense his presence")
See Aura ("see his aura")
Detect Psionics ("sense psionics in him")
Sense Magic ("sense his PPE")
Remote Viewing ("or remotely view him")
The only difference I can see between these lists is that Nega-Psychics are explicitly protected against clairvoyance (would probably make great assassins) while Psi-Nullifiers are not.
While it does mention that Empathy/Telepathy is a vulnerability for Psi-Nullifiers, they start with Mind Block Auto-Defense so it's pretty much a pointless vulnerability. The only advantage I can see here is perhaps if attacked by Block Breaker, a Psi-Nullifier could be rendered defenseless whereas perhaps Block Breaker would not work against a Nega-Psychic's "closed to the supernatural".
In addition the the specific, the Nullifier is "closed to other psychics and location and sensing magic". This seems like it would cover less than "similar sensing powers" which is not limited to magic/psychic.
On the other hand, Nullifiers are also impervious to magic which "dominates or controls a person", I don't think Nega-Psychics have that benefit. I think a Nega-Psychic would have to spend PPE to use their "Disrupt Magic" ability to prevent a control/domination spell from working against them.
I guess a Psi-Nullifier would too though since it's a reflex to expend ISP against magic cast at them, but even if they did not disrupt the spell (the mage spent 6 more PPE than necessary to counteract the reflex) it would still not work on them.