One of the main disadvantages of the camera is related to the telephoto lens of the dual cameras. That telephoto lens is a great option, but the main downsides are that the pixels of the telephoto cameras are smaller measuring 1.0 microns and the lens is an f/2.6 aperture lens, relatively very slow in phonecamera's terms. This means that if you intend to shoot with the 50mm lens, you'll have to consider its limitations. It will definitely be much worse for low-light photography compared to the wide-angle lens that has larger sensor pixels (1.25 microns) and faster f/2.2 aperture lens. The wide-angle lens isn't that exciting either to be honest, but this is an affordable dual-camera phone, so I expected a lower-spec setup.
For those of you who don't know what the aperture means. The aperture is the hole from which the light passes through the lens to reach the sensor. IF that hole is bigger, more light can pass through it. The number after the f/ symbol represents the size of the aperture. Now, the smaller that number is, the larger the aperture size (so f/2.0 is larger than f/2.6, etc.).
Regarding the pixels, larger pixels means that more photons of light can be captured in each photodiode and the results is better image quality and improved low light performance. The Xiaomi Mi A1 doesn't excels in neither, which is the reason why I am quite disappointed with its dual-camera configuration.
If you intend to buy the Mi A1 (5X) because of its dual camera, it's important that you'll be aware of those shortcomings, so you won't think that you get the same dual-camera performance as some of the high-end smartphones out there, this isn't the case here. So when it comes to low-light photography, I don't expect any glowing results, neither should you.
I would be happier to see a telephoto lens with an f/2.0 lens, this would be great (not asking for faster at that price). If you care about the low light performance of the camera, you should probably be looking elsewhere, but those phones with brighter aperture also cost more. Don't get me wrong, you can capture very good images in daylight, the main problem will mainly be when it starts getting dark. Also the real optical bokeh effect when shooting closeup shots will be less prominent due to the slower aperture.