I took Mass Frog, just for grins, on my Wis-based caster, and it's actually not that bad. I have it landing reasonably well in...well, everything except the new content. It is pretty useless in EE Storm Horns quests, even with a near-max Wisdom and a Transmutation item equipped.
However, I've discovered that it's Spell Penetration check is all borked up, making it it useless against things with even moderate Spell Resistance.
Instead of caster level of 25+, it's cast at a caster level of 8. E.g., compare Implosion and Mass Frog:
(Combat): You begin to cast Implosion at level 29.
(Combat): You roll to see if you can penetrate Blood Tide Sharpshooter's dodge. You roll a 6 (+37): spell penetration success!
(Combat): You roll to see if you can penetrate Blood Tide Sharpshooter's dodge. You roll a 19 (+16): spell penetration success!
21 points of difference in Spell Pen matters. I've already bug-reported it, but if you were thinking about taking it, keep this in mind.