I think there is some valid criticisms of the skill. I would say it's much worse than Nyx's for two primary reasons: 1) It's channeled and 2) it deals no damage.
While it is great for offsetting Lion's horrendous mana costs, I do think that it's value in a game decreases the later the match progresses. Someone on your team will be picking up mana boots (barring the extreme case of drafting a mana independent team) so you can often expect a quick burst during combat just as much as your opponents can expect your drain to be offset by their own boots. Most mana dependent heroes will likewise have soul rings, magic wands or even black king bars that can interfere with your ability to deny them mana. And the later the game goes the greater heroes' mana pools become not to mention their increased mana regeneration.
And in team fights, damage is more important than mana drain. Sure, having no mana will stop heroes from casting spells which can reduce their impact but dead heroes can't cast either.
It looks like it could excel in the laning phase, however, which isn't to be underestimated as most Dota games are won during that time (in my experience at least).
, well more like implied, yeah totally you will win against most popular mids with this build(If you don't get ganked into the dirt).
