I daily drive graphene. It's very good and I haven't had any issues with it. I think the security/privacy claims are somewhat overstated but it's definitely better than stock and gives you a lot of freedom in terms of how you mitigate advance of the Google empire.
I'd be interested to hear more about the security/privacy overstatements.
It depends on your threat model. If I'm trying to avoid Google-controlled hardware or firmware, it's bad. If I simply assume that the software or hardware is compromised, I have no escape from tracking, unlike with hardware kill switches.