How will Itachi notice exactly? He's not a sensor. The attack won't give Mu's position away immediately if he's directly above or behind him, which isn't that hard to do with Mu's skill set. And by then it will be too late. Itachi is a sitting duck in this fight if he uses Susano, which he probably will. Mu is a bad match up for him.
Why you running in circles now gentleman?
I several times already gave explanations as to why he would spot Muu,not for sensor abilities but for freaking blessed eyes that grant him reflexes that a normal shinobi can only dream of
here it's not about Itachi spotting muu,as it's as clear as day it won't happen,here it's about itachis reaction time after the former becomes visible,reaction time which i recall being beastly,something like reacting to real lightning isn't something any shinobi can boast about U_U
And no,just no,Itachi isn't any sitting duck,please stop the silliness at once
Now you said Muu goes airborne in the proximity of Itachi,and this is what happens in sequence
1)Itachi immediately notices the foe(reaction time)
2)Muu starts molding his dust attack(reasons i already addressed in my previous assessment),so the jutsu won't come out already prepared like you make it out to be,and in making something time/instants are passing by
3)Itachi or erects susano'o or ignites the tsuchikage on the spot
4)Muu's corpse dead and Itachi won another fight