Greenfield
Adventurer
First, the Magic Item Compendium is a book full of badly conceived and seriously broken items. Considering how poorly written it was it wouldn't surprise me to learn that the authors didn't look any farther than the item descriptions, without ever looking at the rules on activation or item slots. (Apologies to those who love that book, but most everything in there is a power boost, over powered and under priced magic gear that tends to break game balance. )
Second, the Magic Item Compendium also post-dates the DMG, so again the DMG couldn't have been referring to items from it.
Third, when an implication from one item contradicts the direct text on that same item from the DMG, I tend to go with the unambiguous version from the DMG.
Additionally, since Momento Magica is a separate item that applies to a completely separate group of casters (Spontaneous v Prepared), it's kind of off topic.
By the way, I discovered that text about the Pearl of Power being Use Activated almost by accident, so I know it's easy to miss. I was doing a word-search on the DMG PDF, and that one was the first reference. Sometimes it's shocking to discover that items and spells don't actually work the way most people play them. (For example, look at Mirror Image: The caster can only swap places with images on their Move action. If someone manages to hit them, and thus discover which one is real, they can continue to target the real caster for the rest of the round. Same for anyone able to observe the hit, if they can act before the Caster can take a Move. In short, it isn't always a dice roll. )
Second, the Magic Item Compendium also post-dates the DMG, so again the DMG couldn't have been referring to items from it.
Third, when an implication from one item contradicts the direct text on that same item from the DMG, I tend to go with the unambiguous version from the DMG.
Additionally, since Momento Magica is a separate item that applies to a completely separate group of casters (Spontaneous v Prepared), it's kind of off topic.
By the way, I discovered that text about the Pearl of Power being Use Activated almost by accident, so I know it's easy to miss. I was doing a word-search on the DMG PDF, and that one was the first reference. Sometimes it's shocking to discover that items and spells don't actually work the way most people play them. (For example, look at Mirror Image: The caster can only swap places with images on their Move action. If someone manages to hit them, and thus discover which one is real, they can continue to target the real caster for the rest of the round. Same for anyone able to observe the hit, if they can act before the Caster can take a Move. In short, it isn't always a dice roll. )