GoPro might be the undisputed leader in the action cam market, but its cameras are not without weaknesses. The greatest of those at the moment is age: GoPro's topcamera was released nearly two years ago.
The YI 4K Action Cam kicks the cane right out from under that elderly camera by using the newest versions of the tech found in the Hero4, including an Ambarella A9SE75 chipset, a Sony IMX377 image sensor and a high-speed Broadcom BCM43340 dual-band Wi-Fi module.
These specs translate into a camera that has the same shooting options as the Hero4 Black, such as recording high-bit-rate 4K-resolution video at 30 frames per second (fps), 1080p at 120fps and 720p at 240fps, but it runs cooler and has better battery life. The performance is so much better that YI even put a touchscreen on the back -- something only available for the Hero4 Black as an attachment or on the step-down Silver model.
On top of that, the YI 4K is $250 (roughly AU$330 or £230), around half the price of Hero4 Black, which is still selling on GoPro's site for its original $500 (though Amazon has it for about $70 less). Having high-end components doesn't guarantee great performance, but in the case of the YI 4K the result is an excellent little camera and a lower-cost substitute for a GoPro Hero4.
YI has continued to issue firmware updates for the camera, too, improving performance and adding shooting options. This includes a flat color setting for easier color adjustments when editing and an "Ultra" resolution setting that, like GoPro's SuperView setting, takes a 4:3 aspect ratio video and digitally stretches it to 16:9 to get more of a scene top to bottom in your shot. The complete list of capabilities is extensive to say the least and is available on YI's site.
Unfortunately, what it doesn't correct for is the amount of chromatic aberration (purple fringing) around high-contrast subjects, such as the buildings against the sky in the above video. In general, you probably won't see it when squeezed down for viewing on a smartphone or tablet. But blown up on a computer screen it's easy to see. Also, like most small-sensor cameras, highlights can easily be blown out, costing you details in bright scenes.