As Shadows you can always deploy ALL your fighters before a battle.
If Hyperspace is allowed you can have all of them waiting in hyperspace as they can come in normal space at will.
The dispersal Tube only allows you to deploy your fighter at range 30 during play (main ships firing phase so no movement nor firing for fighters launched in this way). And this is instead of "classical" firing.
In a short way it is :
Shadow Fighters rule is before play (Deployment Phase),
Dispersal Tube is during play (Firing Phase).
If Hyperspace is allowed you can have all of them waiting in hyperspace as they can come in normal space at will.
The dispersal Tube only allows you to deploy your fighter at range 30 during play (main ships firing phase so no movement nor firing for fighters launched in this way). And this is instead of "classical" firing.
In a short way it is :
Shadow Fighters rule is before play (Deployment Phase),
Dispersal Tube is during play (Firing Phase).