Obviously getting a bit long in the tooth now, but still a solid phone at a decent price. Apple has confirmed it will get iOS 12 so still good for updates for the foreseeable future.
Key Features
4.7-inch (diagonal) Retina HD display with 1334-by-750 resolution
A8 chip with M8 motion coprocessor
8-megapixel iSight camera with Focus Pixels and True Tone flash
1080p HD video recording at 60 fps, and slow-motion video recording at 240 fps
FaceTime HD camera
Touch ID fingerprint sensor
4G LTE and 802.11ac Wi-Fi
I think iPhone 6 is showing its age and iOS 12 is only going to make it worse.
Wouldn't recommend anything older than 6s.