how's their update schedule for Security fixes and OS versions?

How botched are their security lockdown of their phones compared to the Nexus line?

Can't seem to find a list of CVE's fixed with each update (not in their changelogs, that they only post on the forum...) , based on that, they do not fix known security problems.

I was waiting for the Pixels, but the OnePlus 3 looks awesome for the price! How is the camera on that phone? I remember researching OnePlus 2 a while back, and it was the camera that killed it for me.

But are they still doing that ridiculous "invite-only" buying model? I really wanted to get a OnePlus One when it came out but they wouldn't ever let me give them money for one.