[airgreen]

I guess the downside with Chinese version of mi boxes is not being compatible with 4K Netflix, but the 4K TV, possibly Samsung KS7000, I'm buying will have build-in Netflix anyway.

Could you please recommend what box I should buy?

I would NOT recommend buying a Chinese 3S and hack around with it. You are asking for trouble because Firmware quality is unknown and this is the Key ingredient in any Android box. Plus there is no DRM on these 3S devices. Complete waste of money.

Just use LibreELEC Kodi on any AMLogic S905 of your choosing - Kodi Krypton will actually run better on the S905 MINIX U1 than the AML S912 MINIX U9 - that has no stable, and very uncertain LibreELEC support. Don't get blinded by Tech Specs you will never use.
If you want MINIX - get the U1 - that is a more flexible device with LE & Android.

The only real advantage I can see is 4K HDR on the AML S912 and Android Marshmallow is a little bit quicker, plus MM. Adoptable Storage.
But where is the properly encoded source 4K HDR video content found - locked away behind Netflix and Amazon servers - you need a nVIDIA Shield to access that.

Thanks for the warning on mi box hacking, I'll steer away from that now.
As there are not much 4K HDR content, and the TV is compatible with Netflix and Amazon anyway, so I can live with switching between the box and tv.
There are so many S905 boxes out there, but some seem to be too cheap too unknown, hence I was leaning to MINIX U1, which is an established brand and also available in China for a cheap price.
I've also checked, there are no WeTek Hub available either, so I guess I should go for the U1+Air Mice 2 then?