SuperSU 2.79 stable present on the Play Store and here (from site superSU):
https://s3-us-west-2.amazonaws.com/supersu/download/zip/SuperSU-v2.79-201612051815.zip
Edit insert official link chainfire:
https://download.chainfire.eu/1016/SuperSU/UPDATE-SuperSU-v2.79-20161211114519.zip
I read that to function requires support by the chipset: for example, for now, is supported by Snapdragon SoC 820, 821, 652, 650, 625, 617 and 435 of Qualcomm and requires a firmware update to be enabled. I do not know when miui supported.
The problem of calculator is old "bug" never solved:
https://xiaomi.eu/community/threads/miui-8-and-calculator.33450/
http://en.miui.com/forum.php?mod=viewthread&tid=372264&highlight=calculator
Thanks for the release. On my redmi 3S at the first installation was wrong audio / microphone on phone call, reinstalled again and all function is ok.
The new SuperSU-v2.78-SR3 is here: https://download.chainfire.eu/1012/SuperSU/SR3-SuperSU-v2.78-SR3-20161103171345.zip
In redmi 3s (normal without b20) I installed last night 6.9.29 and noticed that some app does not respond immediately, they bring more to start or to load, about 0,5-1 second.
On my Redmi 3s until the 6.8.25 flash rom and the smartphone is switched off before finishing.
I switch on, TWRP reflash rom and is successful.
With the last 6.9.8 flash rom immediately.