The Mountain View company launched Android One in 2014. And it did so with the intention that its operating system, Android, would work more fluidly on mobile devices with reduced performance at the hardware level. Android One is actually a 'program' whereby smartphone manufacturers establish a direct relationship with Google for the from software of a certain model. And with certain conditions.
This program forces smartphone manufacturers to leave the operating system practically the same as Android Stock; that is, without modifications. Google only allows them to introduce very small improvements such as custom applications for the camera, among others. Another key factor of Android One, which differentiates the operating system that we use on practically any mobile phone, is that the manufacturer has to to guarantee 24 months support. That means that we are going to enjoy, yes or yes, three versions of Android different and all the security updates that arrive every month.
Android One is the closest thing to Android Stock, but on non-Google phones
Manufacturers like Xiaomi or Nokia –among others- have opted to introduce Android One on some of your devices. And in the case of Xiaomi it is especially notable that Android One guarantees an experience much closer to Stock than your MIUI customization layer. That translates into more storage space available to users, because there is not as much bloatware, and greater fluidity on devices with not excessively powerful hardware.
On the other hand, it also implies faster updates, and guaranteed. Because the customization is much less, the manufacturer has to make adaptations to the Android source code, yes, but they entail much simpler work. Therefore, although the updates are not direct from Google as in the Nexus –years ago- or in the Pixel, they depend on the manufacturer but they arrive much faster.
There are disadvantages, obviously. By being Android One a slightly personalized version, there are specific functions that smartphone manufacturers add in their customization layer that, on these devices, do not exist. However, most of the differences in Android One compared to modified versions are advantages. At the level of fluidity and support, leaving the user to carry out the customization if they want, for example, with a launcher.