The problem with Tear of the Goddess
Tear has an interesting concept of delayed power that is held back by how the services it is intended to provide are juxtaposed to the demands that it makes. This is despite being reworked in the mage update to alleviate that problem.
Let us briefely overview the main mage mana items:
bought for providing your mage the full package. Need AP? CDR? Mana? It's all there
bought for the sustain and high HP it provides to close range and top lane mages
bought if your champion can provide it with the spam necesarry to stack it. Good slaves are rewarded with mana and AP.
Each of these items are bought for providing the mage something necessary: mana. Necessity items should be chosen based on what you think your champion needs to function. A good example of this principle played out properly is the current jungle items. Each is chosen based on what your role will be, and a few champions have their pick if they can play multiple roles. Tear's functionality though, is a demand. Demands are typically made of damage items, since they are based onthe champion's attack or spell patterns. For example, 
clearly has on hit synergy and 
is clearly good for burst combos.
Consider the top archangel staff users:
These champions are not similar enough aside from being mages who can rapidly tick down their mana to be sharing a starting item. Rather, they are treating it as more of a damage item/stat stick that only they can access. The only one who truly gains personal benefits from the item is Ryze due to having actual mana scaling.
TLDR; tear promises services like a necessity item, but makes demands like a damage item which will always make it an awkward niche purchase that doesn't do what it is supposed to.