I have just tried it out. HotSpot established with mobile phone (Nokia 7.2, O2, normal LTE). I didn't notice any difference to the normal (very fast) W-LAN.
However, I also assumed beforehand that this was the case. I bought the device (also) to use it on the road, and most of the time it will have to run via a mobile hotspot.
I'm also quite taken with the device otherwise. It's intuitive and fluid, and most apps are available in the store. What I miss is Sky Ticket. But Xiaomi can't do anything about that ...

12-16mbit is completely sufficient. For HD quality