I’ve used it for almost five years, flashed it myself on my FP3. I disabled microG and I’m very careful & strict about what I install on my phone, also their Advanced Privacy set of tools is pretty good. For my threat model is more than enough and I am very happy overall. Never had any serious issues, or even mildly serious ones tbh, despite people yelling about Android security updates arriving late. There was an outage in their cloud services in October that required a complete revamping of their server infrastructure and that took months but I don’t use their cloud so I wasn’t affected at all.