There are several Kanohi that rely on elemental Psionics to some degree. Some of these masks seem to make each other redundant, but I hope to show that this isn’t the case.
In order to discuss the differences of some of these masks, first the distinction has to be made between Rahi and non-Rahi.
What Matoran consider to be Rahi or not does not completely align with the “true” definition. They think that anything that is significantly different from them physically is a Rahi and level of intelligence is not taken into account. However, the “true” definition is based on intelligence. This is how a Toa of Psionics would be able to tell the difference between Rahi and non-Rahi, presumably from the fact that most Rahi don’t have much of a mind at all. Rahi are not intelligent enough to make moral decisions, which is why Shadow Leeches cannot affect them.
While the two definitions of Rahi are largely similar, below is a short list of species and beings that differ between them.
Artakha Bull - Due to their high intellect, Artakha Bulls are only considered Rahi in the view of Matoran.
Keetongu - Keetongu can speak Matoran and cannot be affected by the Mask of Rahi Control, therefore he is not actually a Rahi. He is only considered a Rahi in the view of Matoran. Keetongu does have a sense of morality, enough to distinguish good and evil.
Nui-Kopen - Lewa used his Komau on a Nui-Kopen, implying that it is not actually a Rahi.
Rahi Nui - Onewa used his Komau to inflict a Psionic attack on Rahi Nui’s mind, insinuating that Rahi Nui is not an actual Rahi.
Tahtorak - Tahtorak can speak Matoran, implying that it has a high enough intelligence to not technically be a Rahi.
Toa Hordika - Toa Hordika are Toa mutated by Hordika venom and not considered Rahi by Matoran. However, because Rahi are actually determined by intelligence, they are (at least partially) Rahi mentally and can be influenced by a Makuta’s power of Rahi Control.
Visorak - Visorak are called Rahi by Matoran, although they do not consider themselves to be. They are quite intelligent, suggesting that they might not actually be Rahi, although they can be affected by Rahi Control. Visorak are probably right on the border of what is and isn’t Rahi.
This section discusses the Mask of Psionics’ mind control, the Komau, Mask of Rahi Control, and Mask of Insect Control.
Toa of Psionics are described as having “limited mind control (cannot make someone do something that is against their pre-existing moral code).” The wording suggests that the reason Psionics’ mind control is limited is because it cannot make someone go against their morals. Although speculative, the Komau could have this advantage over an elemental Mask of Psionics. This wouldn’t make the Komau overpowered, even when worn by a Makuta, because it can only work on one target at a time and willpower is a factor. This also wouldn’t make it immoral, as it still has the capability of being used for good.
The Komau is said to not be able to work on most Rahi, but considering that the Matoran usage of the term is probably intended here, it should be understood as not working on any actual Rahi. The only noted exceptions for the Komau are Krahka and Keetongu, which, as established prior, are not actual Rahi. Whatever the Komau and Mask of Psionics can control, the Mask of Rahi Control and Mask of Insect Control cannot, and vice versa. This makes even more sense if the Komau can in fact make someone go against their morals since Rahi don’t have any morals, but Krahka and Keetongu do.
Rahi Control and Insect Control (which is a possible mask power), are forms of mind control. When compared to Insect Control, the details on Rahi Control are contradictive and unclear. Insect Control can work on multiple targets at once so that the user can control entire swarms. One quote says that Rahi Control can work on multiple targets as well, while another implies that it can’t. Some say Rahi Control can work on insects, only not as well as Insect Control, and one says it can’t work on insects at all.
Possible explanations include:
Rahi Control can work on all Rahi, even insects, but only one at a time, while Insect Control can work on only insects, but more than one at a time.
Both Rahi Control and Insect Control can work on multiple targets at a time, but Rahi Control cannot work on any insectoid Rahi, while Insect Control works only on insects.
This section discusses the Mask of Psionics’ telepathy, the Suletu, and Kraata of Mind Reading.
Most if not all Kraata powers can be Kanohi, meaning that Mind Reading could be a possible mask. However, the Suletu, Mask of Telepathy, already exists, which isn’t just mind reading, but actual two way communication. Makuta have the power of Telepathy, which was said to not be a Kraata power, but I would suggest that it is. The reason that Kraata and Rahkshi of “Telepathy” are effectively only capable of mind reading is because two way telepathy requires a level of intelligence greater than or equal to that of Matoran, which can be partially determined by the ability to speak the Matoran language. This also means that Rahi are not capable of Telepathy. Krana Za and Krana-Kal know Matoran, but cannot physically speak, and so require Telepathy to communicate. Even the Morbuzakh can speak Matoran, and Oohnorak gained this ability through its telepathic power. Kraata, on the other hand, are not intelligent enough to speak, with the exception of the seventh stage. Because we have never seen a seventh stage Mind Reading Kraata in story, it’s impossible to say whether it would be capable of actual telepathy. This way, this gives reason as to why Makuta have Telepathy and does not create a redundant Mask of Mind Reading when the Suletu already exists.
The Mask of Psionics’ telepathy is just as powerful as that of the Suletu, meaning both can deliver mental noise to their targets to prevent them from concentrating, have a limited range (presumably in range of eyesight), can project one being’s thoughts onto another, but cannot affect memories. However, this doesn’t mean they are the exact same, making it open to some interpretation. While they would be equally powerful when applied to one target, it is unclear whether Psionics can work on more than one target at a time, but the Suletu can allow its user to hear multiple beings’ thoughts at once (BIONICLE Legends #5: Inferno, Chapter 3, pp. 40-41; BIONICLE: Makuta’s Guide to the Universe, “Toa Inika Kongu,” p. 41). While Kongu was not able to telepathically talk with multiple beings at one time, it might be possible when given enough experience with the mask.
This section discusses the Mask of Psionics’ telekinesis and the Matatu.
The situation with Psionics and the Matatu is near identical to that of Psionics and the Suletu. While there are conflicting quotes on whether the Matatu can move multiple objects at once, this is the only obvious advantage it could have over Psionics.
This section discusses the Mask of Psionics' illusions, the Matatu, and Kraata of Illusion.
The Mask of Psionics is capable creating mental illusions that can fool all five senses, but not technological systems (which would include robots like Vahki and Maxilos).
Illusion, being a Kraata power, is also a possible mask power (although it would have to have a different name because the Mahiki is already called Illusion). A Kraata’s and Psionic’s illusions differ from the Mahiki’s in the fact they are mental, while the Mahiki’s are physical. This means that a Mahiki should be able to fool technological systems.
Similar to Telepathy and Telekinesis, the only obvious advantages that Kraata Illusion could have over Psionics is being able to affect multiple beings at once and/or multiple illusions at one time.
This section discusses the Mask of Psionics' 'invisibility', the Huna, and the Volitak.
The Mask of Psionics is capable of masking the user’s presence from beings, but not technological systems. The Huna and Volitak, on the other hand, should be able to hide from technological systems (unless the system uses sonar, since the Arthron can see through them).
Overall, the Mask of Psionics gives the user a Toa level control over a range psionic abilities, but (presumably) can only use one at a time and only on one target at a time, while more specific masks can affect multiple targets at a time or have some other advantage.