All these videos were from MIUI 9 Beta ROM running on Mi6 in China. So here are the samples:
App launch speed:
Compare that to the current MIUI 8 speed:
Smart app launcher:
Simplified home screen editing:
Now you’re asking “But how does it run on lower end phones?” Well MIUI Forum users also have that answer ready for you! See here how MIUI 9 runs on Redmi Note 4 (SD).