I have 21 Horridon kills, 6 normal and 15 heroic and I have only seen the trinket drop once ever (on normal), which went to our druid healer. I roll on this boss every single week, it's the only item on need on him and other than rolling a ring one time I've rolled gold all the rest.
However the Lei Shen healing trinket will not stop dropping on heroic. I don't think we ever saw it on normal but it's basically dropped on ever heroic kill but one, we just have to keep disenchanting it.