I am a huge fan of autocannons. My first Autocannons were with my Night Lords back in 1999. Back then you were able to take veterans as troop choices and elites if you played Night Lords. So I would take 9 units of 5 with two autocannons in each, and they would all be able to infiltrate. then a few havocs, a fun HQ, and there was my army. Rhinos never survived rd 1. It was fun.
Then there is the psycannon. Same Strength as the Autocannon with shorter range but a higher rate of fire and it rends. Love it, need it. Combine that with autocannons with psybolt ammo on your dreads, why not go grey knights.
So I bought a bunch. I loved the purifier. I quickly built 4 squads of 10. Was fielding Coteaz and Crowe together. Figured I was done. Moved forward to using strike squads and some terminators. However I had forgot one thing when I bought the purifiers and had put them together.........
OK, back to work........ 10 models, down 25 to go.