I bought it at the official german Xiaomi Online shop. It's the X3 NFC.
Btw. I noticed the Huaxing panel can also keep sunlight mode activated for a longer time period than the Tianma panel.
Same setup side by side holding both phones under direct sunlight and using them (scrolling around, starting apps etc.).
The Tianma panel seems to have a more aggressive thermal management and turns off sunlight mode more quickly, making it less readable than the Huaxing panel with regards to maximum brightness level.
This is just my subjective observation though.
Thanks for your detailed feedback, I guess it also affect the battery life then.
My parents received it, the manufacture date is 2012.12 which is pretty recent. The first batch might have the Huaxing panel (for marketing reason; youtube reviewers, etc...) and the later bunch the Tianma one (for cost reason). I might be wrong though. I will check it once I have it in hands and comeback here to post.