@Luv r labs I have both the mia and the smart one. They both do an excellent job of cleaning the face.
The difference with the smart one is that it adjusts the speed automatically. You start out on the forehead with a strong cleaning process, then go to the nose, mouth area with the same strong cleaning process (beeps when you are to move from the forehead to the mouth). Then the speed is reduced for the cheek area, for a more sensitive cleaning. It also tells you when you need to recharge and when to change the brush head.
My Mia 2 has just one speed, but cleans very well.
I use the smart Clarisonic for the evenings to ensure I get all my makeup off.
I use the Mia 2 in the mornings when I am only removing any residue from the night (creams, lotions, etc.).
Hope this helps!