Well, you are true, SJCAM M20 is not 4K camera. Its resolution is 2880×2160 px, but you must know that problem is not in a sensor – it has Sony IMX206, 16 MP sensor – but the Novatek NTK96660 chipset, which is not capable to render 4K video. My conclusion is that, regarding the sensor quality, and the price of the camera, it should be a good deal.