This is a simple reference for those confused of the various versions that may be available in the market. Credit: https://forum.lowyat.net/index.php?showtopic=3561305&view=findpost&p=84058836 and koshergoy.
1-MDZ-15-AA and MDZ-16AA- only 1gb ram and 4bg storage
2-MDZ-16-AB-(International version) 2gb ram/8gb storage/chipset-Amlogic S905X-H Quad core/chromecast built-in/google playstore
3-MDZ-18-AA-(Xiaomi TV 3 Enhanced)2gb ram/8gb storage/Chipset- MT8693 Hexa 6 Coree
4-MDZ-19-AA-(Xiaomi TV 3S)2gb ram/8gb storage/chipset-Amlogic S905X-H Quad core
5 MDZ-06-AA/AK which is 1gb/4gb MTK chipset and MDZ-09-AA/AK 1 or 2GB/4GB MTK chipset
Only models 15-AA (small square cube) and MDZ-18-AA are white in colour.
The remaining models conform to the common black, low slung, round edged profile. The remote layout for MDZ-16-AA / AB have the additional voice button.
ONLY MDZ-16-AB (international version) has ANDROID TV, the rest all run the Chinese UI as default. Hope this list helps.
It should be noted that Xiaomi never ever promoted any product except MDZ-16-AB aka MiBox3 as suitable for sale outside PRC.
With the exception of this specific model, all other Xiaomi boxes are intended exclusively for Chinese domestic consumption and are subject to the numerous software constraints dictated by their government.