So, the first half of the effect of the Pearly White Spindle Aeon Stone reads "When you invest this aeon stone, it slowly starts healing your wounds, restoring 1 HP every minute." We'll ignore the second half (because everyone already does)
A friend and I are in a disagreement about whether two or more attuned Spindles would fall under the "Duplicate Effects" clause; "When you're affected by the same thing multiple times, only one instance applies, using the higher level or rank of the effects, or the newer effect if the two are equal. For example, if you were using mystic armor and then cast it again, you'd still benefit from only one casting of that spell. Casting a spell again on the same target might get you a better duration or effect if it were cast at a higher rank the second time, but otherwise doing so gives you no advantage."
One side argues that these are not duplicate effects because it's not a condition, bonus, penalty, or ability being applied to the wearer, but multiple sources of healing happening in the same way. (comparable to drinking two healing potions, or being affected by two Heal spells)
The other side argues that because they are the same effect, reoccurring at the same intervals, they are duplicate effects. (comparable to a dragon instinct barbarian getting additional fire damage being unable to get the benefit of a Flaming Rune, or a Sylph character with the "Swift" feat doesn't gain the benefit of the Fleet general feat)