Used 'em once; 3 wracks, acothyst w/rifle, haemy w/rifle. They managed to drop two rounds on my opponent's termie libby warlord, which he LoS'd. After that they didn't hit a damn thing all game.
Never again =(
EDIT: Regardless of my lacklustre dice rolls, my issue with them is even if you manage to target a warlord or other IC, they can just Look Out Sir. So the best use is to target special weapons, and honestly I'd rather use the points to try take out the entire unit.
I dedicate these deaths to Odin Allfather, Spearshaker, One Eye.
Fleet Shadowmaker - Kabal of the Dying Sun; Cult of Marrow Excised; Coven of Lambent Hunger
Sons of the Last Breath - Chaos Space Marines
Host of Shattered Purity - Chaos Daemons