Please Buy a Google Pixel Next Time
In many cases, certain vendors' phones would tell users that they had all of Android's security patches up to a certain date, while in reality missing as many as a dozen patches from that period—leaving phones vulnerable to a broad collection of known hacking techniques.
And it gets worse: even your fancy-er high end phone may be vulnerable:
[Security Research Labs’] testing found that other than Google’s own flagship phones like the Pixel and Pixel 2, even top-tier phone vendors sometimes claimed to have patches installed that they actually lacked. And the lower-tier collection of manufacturers had a far messier record.