I like the Magus thus far, but I think the first part of the True Magus is basically mechanically pointless.
"Whenever he uses his spell combat ability, he does not need to make a concentration check to cast the spell defensively."
Since this is a level 20 ability there is no need to worry about multi-classing or those kinds of interactions.
The Magus maxes out at 6th level spells and no longer takes a penalty on his concentration when using spell combat. Therefore his maximum concentration DC is 27 (15+6x2). For concentration checks at level 20 when he gets this power he is already adding caster level (+20)and the lowest ability score mod required to cast the spell (+3 for level 6 spells, +2 for level 5 and 4, and so on).
Assuming he was the worst Magus in the world and had only the minimum int required to cast level 6 spells and took no feats, traits or class abilities to boost his concentration he would still only fail his hardest concentration checks on a roll of 3 or lower.
Even a worse Magus who lacked the int to cast 6th level spells, only 5th would need a 2 or 1 to fail his hardest concentration checks.
I can understand it flavor-wise, but mechanically it really provides no boost to anyone playing a decent Mangus