In my opinion, they're pretty shoddy design. Not well balanced with other options. For instance, compare and contrast Ioun's blessing (level 3, +2 item bonus to all skills and a daily for a further boost which is untyped, group-wide, and encounter duration) to the following:
- Crown of Doors (level 6): +2 item bonus to Perception checks to find secret doors
- Phylactery of Divinity (level 6): +2 item bonus to Heal and Religion checks
- Circlet of Authority (level 7): +2 item bonus to Diplomacy and Intimidate checks
- Crown of Leaves (level 7): +2 item bonus to Nature and Insight checks
- Diadem of Acuity (level 8): +2 item bonus to Perception and Insight checks
- Headband of Perception, paragon tier (level 11): +3 item bonus to Perception checks
WTF??
Yes, head slot is largely filled with subpar items; it's clearly not intended to be one of the big three. But the boon is slotless, which makes the comparison even more unfair in the wrong direction. And the cost difference is massive.
They're a fabulous idea. But whoever actually statted the ones they've released so far should literally be shown a pink slip, they're that bad. Ioun's isn't the only one; Pelor's, Sethanine's, and especially Corellon's are also absurd for their level.
If you treat the very high power level as not being merely "paid for" by the item's cost but also by a specific need to earn it - not just as fluff text but as a real, serious mechanical requirement - then you might be able to justify releasing them as written. But even then I'd have to think long and hard before doing so in my game, and I advise the same.
