I've been running 15 Chosen with Mark of Khorne backed up by a Khorne Lord. They hit hard, but they aren't easy to reposition and i've struggled with going through screens, which means they normally get hit with whatever is behind. I've changed my army up, but kept 5 in to be backline objective holders that can swing back at any outflanking or teleporting shenannigans.
When I run them in the future, I think i'll run them undivided as they normally get targeted. They aren't very tanky so I tend to lose 4 to battleshock a game, I think rerolling 1s isn't worth having 140 points just run away when they could just be immune.
edit: Also sod Finecast Mine are a mix of Chaos Knights, Forsaken, miscellaneous bitz and a lot of Greenstuff.