Blue
Ravenous Bugblatter Beast of Traal
Conversely, at many tables the number of encounters per day is mostly under control of the DM and will likely stay the same. So it will allow the casters to nova more in the same number of encounters.They seem like they would be quite powerful to have around, but would extend the casters to more encounters. I might suggest a minor potion to grant 1d4 levels of spells and a major one to grant 1d6+1. Then let the player choose what spells and if he wants a few low level or one high level, depending on his roll.
It's like scrolls, but with more flexibility. I do get a little wary when resource-limited classes are given more resources, but at-will primary classes aren't given more rounds of combat so that they can do more as well.