Rage Mastery and Rage Gifts -- Redundant? Not really. While Merits and Gifts are intimately tied to Rage and the Gauru form, and sometimes produce similar (or even identical) effects, the means by which they do what they do are very different. Like all Gifts, Rage Gifts are spiritual tricks hard-won from the denizens of the Hisil, with higher-level Gifts reflecting the werewolf's Renown and standing among spirits and Uratha. Thus, Rage Gifts often exceed Rage Mastery's effects (especially at the higher levels), creating more powerful effects more efficiently. Meanwhile, Rage Mastery is an intensely personal practice, developed by a werewolf through practice and intimate familiarity with the roiling anger inside her. She doesn't have to impress the spirits or attain Renown to learn these techniques, and in theory relies solely on herself -- though the vast majority of Uratha that learn these Merits have werewolf teachers (just as it's a lot easier to, say, learn Spanish from a teacher than to pick it up from only a Spanish-English dictionary). To reflect this, Storytellers may want to charge 150% normal exp (9 exp as opposed to 6) for Rage Mastery techniques picked up without a teacher, or enforce other requirement -- for instance, using the Gauru form more often than is wise while "practicing." Despite the difficulties involved in learning and applying Rage Mastery, and its more modest effects compared to Rage Gifts, its techniques appeal to enough werewolves to keep the practice going. As discussed before, one can learn Rage Mastery techniques from other werewolves or intense practice, without having to kowtow to spirits; in addition. Rage Mastery can be freely used in times that Gifts are weakened or inaccessible (such as areas where the Gauntlet is too thick or Barrens), as well as when the character is depleted of Essence or Willpower.

The Gauru form is the Uratha race's ace in the hole, a tank of tooth and claw and muscle brought to bare under the most circumstances. Already spirit-warriors with an array of powerful forms, the Form of Rage makes werewolves even deadlier. However, this extra power comes with a price, as Uratha that court the Gauru risk loss of self-control.
However, some werewolves can tap into that wellspring of Rage, and can manifest different abilities than most werewolves in Gauru form. This is known as Rage Mastery. However, even learning Rage Mastery this is dangerous (much less practicing it!), as only Uratha intimately familiar with their primal anger can alter how it manifests. These techniques are picked up through practice, even for those that learn Rage Mastery under a teacher, which means the werewolves that would learn them must assume Gauru form often. This makes them dangerous company, but valuable in a fight.
Rahu of all five Tribes of the Moon practice and teach Rage Mastery, and when used in conjunction with Rage Gifts can become truly formidable opponents. Among the tribes, Blood Talons are the most likely to use Rage Mastery, though some Storm Lords appreciate the greater control it offers. Among the Pure, Predator Kings manifest Rage Mastery so often many credit them with having invented it.

Systems
Below are guidelines for creating Merits -- Rage Mastery techniques -- which allow players to fine-tune their Gauru form's capabilities, gaining new powers or augmenting old ones. Each Rage Mastery technique is a two-dot (●●) Merit. There is a trade-off, however; Rage Mastery is a zero-sum system. Gaining one benefit means losing another. These changes are temporary, and the character always defaults to the "standard" Gauru abilities when assuming that form. She must consciously apply a technique if she wants its benefit.
Use of a Rage Mastery Merit is a reflexive action unless specifically stated otherwise, and only one application of Rage Mastery is allowed per turn. All Rage Mastery techniques are only usable in Gauru form.
Constructing a Merit: Each Rage Mastery technique is a personal thing -- there's no generic list from which to pick. Instead, each Merit is custom-created based on the desires of the character and her player. This is a simple process, but requires thought on the player's part. Upon purchase of the Rage Mastery Merit, the player chooses a desired benefit, then chooses a sacrifice (benefits and sacrifices are chosen from their own lists). Taken together, the benefit and sacrifice form the Rage Mastery Merit. Each combination is set once chosen, and the player can't elect to swap out one benefit or sacrifice for another. However, two contradicting qualities can't be chosen, which is pointless anyway; you can't sacrifice a dot of Stamina to gain a dot of Stamina, for example, though a Merit that trades a Dexterity dot for Stamina is possible (as the effect involves different Attributes).
Uratha may learn more than one form of Rage Mastery (and in fact, most such werewolves have a variety of techniques under their belt). Each Rage Mastery Merit is learned separately, and exists separately from other techniques; it's not part of a graduating, five-dot scale like Martial Arts. However, while techniques can complement each other, and while one can allay the sacrifice imposed by another, technique benefits do not stack with each other, nor do they augment similar bonuses offered by Rage Gifts. When they come into conflict, Rage Gift effects always take precedence over Rage Mastery (though sacrifices still remain in effect, you powergaming schmuck). In other words, you can't learn the Merits Gauru Duration to Strength Dot, Health Level to Strength Dot, and Control to Strength Dot, use them together, and then use Hone Rage (Rage Gift ●●) to toss a city bus at a Beshilu for that one glorious turn you remain in Gauru form. The one exception to this rule is purely durational effects, such as using two different Merits to increase time spent in Gauru form or to offer increased control. However, if you so choose, you can burn the candle at both ends and use techniques with compounding sacrifices.
By all means, feel free to personalize Merit names to reflect the feel of the setting and character proclivities. While an apt description, Health to Armor is a bit clinical. "Blood For Muscle" or "Iron Agony" sound much better, and is likely to reflect the terms real Uratha would use -- they don't think in game terminology terminology, after all.
An Example: After her Storyteller introduces the Merit into his game, Tamika chooses the benefit: control, and the sacrifice: Gauru form duration. Her character may now sacrifice potential turns in Gauru for a clearer head while in that form. She calls this Merit "A Moment's Clarity." She couldn't sacrifice Health for clarity, or sacrifice Gauru form duration for a Stamina bonus, or even reverse-swap control for Gauru form duration -- each of those capabilities would be separate Merits. However, Tamika decides to save up experience points for a Rage Mastery Merit that allows increased Gauru form duration at the expense of Health (which she'll call "Feeding the Beast My Flesh"), to offset the effect of the first Merit.

Benefits
All-Out Attack: By sacrificing all other attacks that turn, the werewolf can make a single claw or bite attack with a +4 bonus.
Attribute Dot: One of the character's Physical Attributes (Strength, Dexterity or Stamina) increases by one dot for a single turn.
Control: For a single turn, the Gauru-form werewolf gains a +2 bonus to Resolve + Composure rolls to perform actions other than rend and destroy.
Defense: For one turn, the character uses the highest of her Dexterity or Wits as her Defense.
Extra Attack: By giving up one's Defense for that turn (plus whatever sacrifice entailed in the Merit), the Uratha may make two attacks against the same opponent in the same turn. However, both attacks incur a -1 penalty, and must involve a claw-claw, bite-claw or claw-bite routine (no bite-bite or use of weapons).
Gauru Duration: The character can remain in Gauru form for one additional turn before risking Death Rage.

Sacrifices
Attribute Dot: The character loses one dot from a Physical Attribute (chosen by the player) for the duration of the combat.
Control: For the rest of his time in Gauru form, the character can't do anything but attack, smash stuff, or move directly from one opponent to the next, and may not make any Composure + Resolve rolls to do otherwise. If he's in Gauru form at the end of the normal form duration, he is at -2 to rolls not to enter Death Rage.
Gauru Duration: The Uratha loses a turn of Gauru form (chopped off the end, of course).
Health: The character loses one Health point. This is treated as lethal damage.
Wound Penalties: The character is affected normally by wound penalties for the duration of Gauru form.