While I do agree that Hexdrinker is VERY cost efficient, its CD on the shield is abusable BECAUSE it's not an active. You can poke it out an inopportune times (for example, while their combo is down) and force the shield to pop, leaving them vulnerable if they do decide to all-in. It's all about you managing their shield, which you can play around since its debuff appears in the tool tips. I highly recommend you try this on a myriad of mages; most of their ultimates (with 10% CDR available early: Fiendish Codex, Boots of Lucidity, or Forbidden Idol) can hit right at or just below that 90 second mark, especially if you start hitting 20% CDR or higher. Play around it. Start spamming those matchups, or go into Custom games with a friend playing that matchup. It's great practice to pick losing matchups in normal games to get used to being counter-picked.