ppl who want brand security and ppl who want uptodate sec and trust google?
I have the nexus 6p, very nice thank you. And this does not look like a better phone, no stereo speakers? what? really expensive.
But its a Google version one product... maybe a version 2 product (Nexus range version 1?).
So... they are probably feeling their way and not expecting too may sales. The next one, the one with an andromeda OS may be the one to look at. The first Chromebooks where a work in progress, they got better.
That said not sure if this Apple business model will work for Google.
On the security side no phone is totally secure, but some are much safer than others. It really depends on who you have after you. Run of the mill threats from criminals? Then Google supplying your OS and patches will do the job 99.999% of the time, as long as the user keeps to the play store and isn't thick. But just like any computer system it will from time to time be breached. All you can hope for is a quick patch.
If you have someone serious after you then all bets are off. Don't kid yourself that your homebrew system is secure against this type of attack. 1st line of attack is to seed a weakness into the base software, the stuff that you use is built on this so compromised. 2nd your phone is connected to a network run by ppl that can be working for any number of players. So the only reasonable course is not to worry too much about the security services having access to your phone or correspondence if they ever want it. After all that's what they get paid to do, and you have expect that they are competent. So protecting yourself against a second order threat is reasonable and you are probably best to go with someone who will suffer damage to their reputation if they let you down (and have good engineers), so Google or Apple basically. YMMV