Can, you can sideload on both orange box or brown box MDZ-16-AB to your hearts's content. Just that the orange box MDZ-16-AB has free trial vouchers and has some pre-installed apps (which can be removed or disabled) To not confuse you or anyone for that matter, just remember all MDZ-16-AB as International version, simpler that way.

Well, Xiaomi have used roughly the same design for its earlier android boxes for years, Its quite a safe bet that the hardware is quite good by now. Most of the problems (which is not alot) I read from reddit for the box seems to occur at 4k resolution streaming but I think it can be rectified with a software update or two. If I were to choose right now, Ill buy whichever is the cheapest.