This maybe one of those things where a choice can be made by the player at first level and can never be changed. It certainly puts a different flavor to the summoner class.
The other thing is the restricted spell lists, which drive me up the wall. Several reasons new spells never get added to any of the lists a "tome of magic" presenting 1 million spell are not for the class that doesn't have it listed. I think an feat something like
"exotic spells" would be useful for each spell a PC removes from his spell list he can add a different spell of the same level from another source. He can do this at each level.
