Magician
Seems odd that the Magician is Cha-based for implementing, but uses Intelligence for Magician's Secret, but then uses Charisma again instead of Int for the Extra Secret feat.
Magician's Secret should spell out the save DC. Since it's an SLA, it's presumably Cha-based, but it should be stated explicitly for ease of use. Ditto Spell Mimicry, although since it isn't an SLA, which stat is used is up in the air.
The RP cost for Counterspell seems a bit low. RP are a lot less valuable than spell levels. Since techniques have neither schools nor subschools, I don't think this ability works at all as written, though.
What's the action cost to use Arcane Surge?
Feats generally look good. A few issues, though.
Modify Metamagic is a bit unclear on how many RP is costs to reduce a metamagic's cost for more than 3 levels. Assuming that people will follow an undefined pattern is a bad idea, and any mathematician will tell you that if the first three numbers are 5, 10, 20, then the next one could just as easily be 40 as it could be 0 or -397 or pi. If there are ever any PrCs that let a spellcaster progress alongside an implementing class, Modify Metamagic will be too strong. The amount of metamagic reduction it can grant is on par with the 10th level capstone of several PrCs (Dweomerkeeper, Incantatrix), with the potential to be even greater with more than 5 RP. Since you get your RP back every turn, the cost is negligible, and since prepared casters apply metamagic at the time of spell preparation, they don't even pay that momentary cost in combat. Finally, the feat needs text to stop it from lowering spell slot adjustments below 0.
Pray for Health is a bit open ended, and can get relatively high level spells at relatively low level (Cha 22 at level 1 is easily achievable, and someone in Sirpercival's High Arcana game is shooting for a Cha of 40 at level 6). The wording implies a replacement of the spell's normal targeting, which may have unintended consequences (like multitarget spells getting the shaft, or spells that target by type being applied to creatures of a normally invalid type). The targeting selection requires neither a willing creature nor an ally, so beware of offensive uses of this ability (at the least, Cure spells on undead, and at the most,
homebrewed offensive healing spells). Finally, healing is a subschool, not a descriptor.
Technique Mastery should say "Choose a
technique for which you have the Favored Technique feat". Also, having an ability modifier of +17 requires a score of 44, which I don't think is intended. Should that requirement be "Primary implementing ability score 17" instead? I would be very careful with this feat , as choosing a single, expensive technique would have ridiculous benefits (spend 18 RP to get the benefit of 117 RP, for example).