I think it is one of those quirky feats, in that it is too good for a feat(does too much), yet in the long run if a wizard for example you probably would of been better served taking empower or some other metamagic feat, and if a fighter better served with power attack etc. At low levels it allows you to play replacement cleric, jsutbe sure to pre-buff your self with some spells targeted at you by a firendly. It also works fairly well if you make your self the obvious target for really nasty spells and then ready actions. Not massively useful unless you tend to fight spellcasters much higher levels than the party. (the evil archmage cliche) This side gets about as much use as counter spelling but hey it can be put on a fighter, and any magic defense can rock when your a fighter.
Also the range blast, basically can end some early boss fights in a very diaspointg fashion for the DM. Ok you face the young black dragon, I blast it with my stored energy for Xd6 doing Y damage. Ok, he's dead.... and you've pissed off his older brother.(yeah that's it) at higher levels it ebgins to look less impressive. And quite frankly the presitge class sucks, so don't take it.