We're about to reach level 11 in my current game and my Binder has become the defacto healer and battlefield controller for the party, with the occasional foray into party tank when the druid is absent. My character is a Binder 6, Knight of the Sacred Seal 2, Intermediate Bloodline (Fey) 2 with an Effective Binder Level of 12 at the moment, next level will up it to 13. The common vestiges I use are Naberious, Haures, Dhalver-Nar, and Zceryll.
My question therefore is, would it be worth it to use the vestige Ipos to up my EBL for Zceryll to 14 so I could increase my summons to Summon Monster VII or would I be better off using a different second vestige and sticking with Summon Monster VI?
Having access to the Avoral, Djinn, and the Movadiac Deva are very tempting I will have to admit, but the limit of how often I can summon replacements makes me reluctant to do this. At level 12 it won't be necessary and I'll have a third vestige to bind to expand my options even further, though then I may be tempted to take the Favored Vestige feat for Zceryll and be in the same situation, where binding Ipos would give me access to the next level of Summon Monster.