First, I love the idea of the class. Now in order to really understand the class you have to realize what you want it to do. Right now it seems like your trying to negate and to manipulate, personally I think you need to pick one devotion. Is the character stopping/manipulate the magic with pure force of will or intimate knowledge of the magic itself (I prefer the later due to the age old belief that you must understand your enemy). It seems to me like your going for the character who sacrifices his own beliefs and learns and understands and even sometimes uses magic, for the greater good to protect them from the "evil" magic users.
Force of will would use wisdom as a primary stat, knowledge would use intelligence. I think what your going for is intelligence, being more skill based and this would also make sense with use magical device, just add a class ability to allowed class level or intelligence modifier to use magical device checks. This would also give them bonuses to knowledge arcana and religion as well as spellcraft. Unless ofcourse your going for a MAD class, with which you could require wisdom and intelligence.
Now, to class abilities:
Eat Magic: I think this should increase every other level, the same as a wizard can cast. So 1st level spells at 1st, 2nd at 3rd, 3rd at 5th and so on. This keeps him in line with a wizard and a little ahead of spontaneous casters. If you go 1 spell level per class level hell be able to lock out a 18th level wizard at 9th level. Another alternative is if you want him a little ahead of the game just bump it by one level, 2nd level spells at 2nd level, 3rd at 4th. I think needing to ready action to eat the spell makes the ability near worthless, but a good idea would be forcing the character to know the spell being cast by using a spellcraft check or at least understand it by using a knowledge arcana or religion check. You don't want the core class ability to be too random. Also I'd remove the reflect ability, keep it to raw damage, maybe allow an element change or die size increase. Make it include spell-like abilities even.
Spell Breaker: Just give them Dispel Magic X times per day with a CL = to their MH levels. At higher level make it become Greater Dispel Magic and then eventually the option of Mass Dispel Magic.
Arcane Breaker: If you allow this on normal traps too, keep it Disable Device. If you want just magical traps and locks, make it spellcraft or a corresponding knowledge.
Track Magic: Absolutely. Love. It.
Resist Magic: I can never decide between save bonuses or SR, the choice is really up to you. Maybe save bonuses at lower level, such as evasion and improved evasion but only with spells, then SR late game.
Null Aura: Either on or off, not controllable. Making it off for the party and on for everyone else, even partially, distorts the class's intent. He doesn't trust other magic users, at all. Period. Maybe at higher level make it so HIS items and things work, not anyone else, including the party.
Suggestions: Shields and medium armor is fine, they can take a feat for heavy. Martial weapons, nets, and whips. Maybe give him a few bonus feats, every 4 levels or so. Hes not supposed to be a front line character, more like a bard or rogue, but anti-caster. Maybe even up his Magic Eater uses per day but make it only spells targetting him, or at higher level even target his party. Either way don't let people make you dilute this class, the idea is amazing. Great Job.