I, also, have never used Horizon before, but came across a blog post by Michael Dawson of NB extolling the virtues of this little known hop. He says it was very clean and neutral bittering properties and the aroma is a mix of lemon/citrus with some grassy notes. It is a dual purpose hop and if I can get my hands on some, the plan is to brew the Imperial Stout with just Horizon acting as a dual purpose hop.
I'll follow up in several months with how it turns out!
K: Waldo Lake Amber, Carmelite Tripel AG, Hopquila Robusto DIPA