How ridiculous is this feat? I created it for some house rules and it saw use in the game for a bit, but because the character multiclassed, his druid was two levels behind, which made his summon one level weaker than it should have been. So, it hasn't really been tested in play.
Master Summoner [General]
Prerequisite: Charisma 13+.
Benefit: When you summon a creature with a Summon Monster, Summon Nature’s Ally, or Summon Undead spell, you may opt to make the duration permanent. If the creature is killed, the creature disappears as normal and this effect immediately ends. As long as this ability is in effect, you do not regain the spell slot used to cast this spell each day; you must keep it in reserve to maintain the effect. You may dismiss the creature and this effect at any time as a standard action. You may only have one such creature permanently summoned with this ability at any given time.
So, am I missing anything? Any obvious abuses? Is it broken, lame, or somewhere in the middle? If it's just a smidge on the powerful side, could it be toned down with adding Augment Summoning as a prereq (which has it's own prereq)?