User blog comment:JmLyan/Zine, the Blade Dancer/@comment-24420226-20160116000300/@comment-7481207-20160116102057

Her mana costs may be low, but so is her mana pool and mana regen. That combined with low cooldown abilities that she wants to use frequently means she can still easily run out of mana. And with the possible 80% CDR from her ult, she'll run dry even faster (also a reason why her costs are as low as they are). Even so, I'll make a small adjustment to her E. (Also, Jax's Leap Strike has a lower cooldown than Blade Dance on every rank except the last, where they are the same.)

The passive makes lifesteal from those heavy AD items less wasted (seeing as she won't basic attack much), and while she would likely not consider Bloodthirster without that passive, Ravenous Hydra IS an item frequently purchased by AD assassins. Since Zine benefits more from longer fights than most other assassins due to her spammable abilities, having the option to increase her sustain beyond a Death's Dance could be profitable. Having the ability to drain decent amount of health from minion waves is also a plus.