User blog comment:Tinhboe/Elder Lizard vs Feral Flare/@comment-5077844-20140814112713

Champions who can stil use feral flare and perform relatively well with it: Warwick, Rengar, Nocturne, Aatrox, Twitch, Shyvana, Xin Zhao, Master yi (and a few others i probably forgot)

Reasons: All of these will scale very hard into lategame. What you do is trade early game sustain and gold generation for a way stronger lategame. It's just a matter of preference.

I think people do it on Rengar because it allows them to build tanky and still do damage with just one item (not to mention rengo's early is painful anyways)