Just noticed that Renegade Flamers are 2pts cheaper than CSM, so a Renegade Cultist squad with 3 of them will have a minor discount over an equivalent CSM one.
Regarding fluff and/or integration with CSM, there are some amazing things we can do here to represent the variety of crazy folks that hang out with CSM:
Thousand Son Thrall Wizards? Supreme Command Detachment full of Malefic Lords and Psyker Covens (bonus points for using it as an excuse to throw in an TS Lord of War like....say....Magnus? Or maybe the Super Chicken Aetos'Rau'Keres?)
Alpha Legion Cultists are covered by their CSM Cultists and the buffs they can get from their CSM brethren. However, a Vanguard Detachment full of Marauders or Disciples (esp. Stalker Marauders) does a bang up job of representing their elite operators. Even "In it for the Money" isn't a problem, because SF folks are huge investments and often have other objectives that they will shift to instead of being tied down in a firefight they're likely to lose. They'll stick hard despite casualties until that 1 comes up, and then they're out. No problem.
Iron Warriors Slave Soldiers? Hello Battalion full of Renegade Cultists backed by Enforcers, big guns, and IW HQ's and specialists. Very easy to build a "Stage 1" IW army where they use bombardments and disposable bodies to wear the enemy down before committing actual CSM.
Dark Mechanicus? Field as many Hellwrights from the Forces of Chaos Index as you want, plus crazy modified Ogryn, Mutant Rabble with bionic parts, and Heretek Marauders, plus as many Daemon Engines, Knights, or Titans as you care to put on the table.
Ironically, we're limited in the ability to represent Blood Pact because we don't have Grenadiers anymore (no carapace units with Covenants or hotshot guns), but regular BP infantry and air support would be fine, plus you can easily throw in CSM Daemon Engines or Helbrutes as Stalk Tanks.
All in all, not bad.
Edited by GreaterChickenofTzeentch, 17 July 2017 - 07:09 PM.