I have decided to explore action cameras beyond the Yi Action camera. The Elephone ELE Explorer Pro ‘4K’ comes with a box-full of accessories, including an underwater case.
While marketed as 4K, the camera is actually only capable of native 2.7K, with 4K recording (only at 15fps) achieved through interpolation. The sensor is the Omnivision OV4689, which at 4MP also suggests that native 4K is not supported. This elproducente article explains the difference between native and interpolation 4K cameras: http://elproducente.com/native-real-vs-fake-4k-resolution-how-to-check/
The lens was very difficult to release from its glued-in fixed focus location. Like many other action cameras this has a very wide-angle 170º lens, which is not ideal for my purposes and has a lot of distortion that needs removing in post-production.
This this time-lapse video tests the camera in low light and sunshine.