User blog comment:Tyrant Belial/Feral Flare tests/@comment-24309189-20140412063801/@comment-1330314-20140415045020

FF + BotRK will wreck top laners, since the combination of hybrid damage + % health damage means you'll shred them no matter what they build against you. Both also synergize with each other in terms of stats, since the combined attack speed both give increases the rate at which you'll apply the two on-hit effects, not to mention the combined healing this combo gives. Not only that, but FF is also excellent at taking down squishies, especially in the late game where they typically have little MR and you have a lot of stacks.

In terms of cost efficiency, Feral Flare is already cost efficient the moment you unlock it, and it just gets better as you play on. BotRK's efficiency scales with the enemy's health, so it'll always be optimal as a late-game purchase, but a is an excellent item to have early on. Upgrade it early if the enemy team is tanking up early or if you're trying to take down high-mobility champions and are struggling to catch up to them.