very valid point. Xiaomi are only becoming more we'll know to the masses now, not everyone is so tech savvy, so won't be so aware.
if Xiaomi were a household name then it would be quite easy to have a break away brand.
if a certain American brand or a South Korean brand decided to break out a budget offering under a new name, everyone would be well aware and would be able to distinguish the brand's without confusion.
But for an emerging brand it's not so easy. the UK is a good few years behind China, Russia and India, you could argue even Spain has a more established market than the UK. So trying to attempt to have two brands under one manufacterer at this moment in time would only cause confusion.
it's perfectly normal to have different variants of the same item in different parts of the world.
Car manufacturers do it all over the world.