I don't agree with some of the cons written about the Xiaomi Redmi 4A camera in the camera category. Just take a look at these camera samples taken by Bikram Rai on miui.com forums. Those shots, according to the photographer, taken with the default camera app at high saturation with normal sharpness and HDR turned on. Other than that, there is not retouching or editing of the photo. Just look how amazing these photos look. I don't care if he tweaked the settings a little bit to make the images look more vivid, these photos just look superb.
Maybe it's not tack sharp in full resolution, but who cares. It's definitely sharp enough, I don't expect it to be a DSLR quality images but these sample images are really close to that. This reminds of the iPhone 7 Plus image quality, it's really that good. It seems that you really need to be a good photographer to make the make the best out of the camera and this guy, Bikram Rai, did an amazing job. I really love the colors, even with extra saturation, the images still look very natural. That extra color just make the images look less dull and more interesting in my opinion. The high resolution just the image look better when downscaled.
I am not talking about the low light performance, because he only show in daylight, but that OmniVision Purecell OV13850 is capable of delivering stunning images. It's not a new sensor. It was announced on November 2013. You can read more about this sensor on Image Sensors World blog. To sum things up, it's a 1/3.06-inch sensor, featuring 13.2MP 4224 x 3136 pixels image resolution. It is known for its very low power consumption (223mW) compared to previous generation sensors. This mean that you can shoot more on a single battery charge. This sensor has 1.12 micron pixels and I can understand why some people here were disappointed with the low light performance. I think that this sensor is optimized for daylight shooting, especially considering that it lacks OIS and uses a f/2.2 aperture lens. I'm sure if it has a f/1.7 lens, it would have been great for low-light photography as well, but for its price, it performs amazingly well.
This guy is a Diamond member on the forum so he is reliable. Anyways, I think that you should take a look at those Xiaomi Redmi 4A sample images as well, before you make up your mind about the rear-facing camera's image quality performance.