The CN ROM itself is not bad, but there are a few things that the EU ROM just does better for a fellow non-chinese user's daily driver phone.
Firstly, this includes vastly extended language support - the best thing you have available to you on CN ROM is an incomplete English locale, where you'll often come across unreadable chinese text in system apps.
Then there's the fact, that the CN ROM offers only a limited Google Play Services implementation and you might find that some components you're used to won't work anymore (e.g. Geocoder API...) - this also extends to a problem with aggressive hibernation of background GMS processes often leading to unreliable notifications from apps that rely on it (which are, basically almost all of them). The last part about notifications can be remedied a bit, by tweaking the system settings and disabling battery optimization for all those apps to make them work better, but it's not perfect and you're going to find yourself missing notifications from time to time.
The EU ROM fixes the problems mentioned above and besides that, there's a detailed list of other additional features that you can find the release thread.
One (major) downside of the EU ROM that I could find at this moment is generally worse camera quality by the camera app (the app in this ROM is slightly different from the one on CN ROM). However, with an unlocked device, there are solutions to this - such as replacing the camera app with the original one from CN ROM, until the devs have had some time to look into it. You can find more details about that by going through
this thread.
Overall, I've been running the EU ROM for quite some time now (weekly build), and it's a solid daily driver. Once I sorted out the camera, there was nothing else that would bother me, resulting in a flawless experience. You'll eventually find some of the issues of the CN ROM yourself, before you get to being able to switch - due to the Xiaomi unlock process, which will require you to wait 7 days before you can unlock your phone.