By the time you get Essence Reaver, you really don't care about mana anymore.
Atleast if you're playing your champion right. This is especially the case for champions who would want to buy it.
The more they level up the less mana is an issue unless you're Anivia or Swain.
Therefore, what purpose does Essence Reaver really serve? I can't think of any champion who'd care about the mana regenerating passive by the time they get the gold to buy it.
The only champion who really would worry about their mana going down is Swain and Anivia, two AP champions.
. The reason most casters do not want to buy a tear though is because of how long it takes to ramp up (it is pretty useless until you get
).
+ 385 Gold = Arcane Blade (1260 Gold)
What about Nasus?
I don't think anyone has mentioned him yet.
I find even mid/late game I am restricted in using my abilities. However with essence reaver, I don't have to worry about using my q, I can just pester my enemies as much as I want. In fact late game using your q gives you bonus mana since the mana cost does not increase when u build your q stacks. So you can spam your abilities pestering the enemies as much as possible without a thought of your mana running out, also when your in mid game the cool-down reduction can help u build your q and there is no harm having more damage and lifesteal.