I do use Conclave and don't have problems with vassals revolting either.
Granted, I didn't have problems with vassals revolting pre-Conclave either, but now I have to do less work to keep the factions down. Previously I had to give out more gold/honorary titles, now I just throw a few council seats to moderately talented faction members and use the generic advisor slots if none of the reasonably strong faction members are good at anything.
It's the only CK2 DLC with negative reviews on Steam, I'm not touching that with a 10-foot pole. I haven't heard anything good about it on the forums.