Multiple summons are borked... i.e. if you level Summon Friend and try to summon a wyvern, you only get one no matter the skill level. Recasting kills the poor Ol' Scaly and summons a fresh one, not an additional one (as promised by the description).
Ergo, learn Summon Demon and forget everything else. Demon rocks. He's my ugly, predatory, eviscerate-you-while-you-sleep best friend.
