At high angle of attacks, the prominent problem is the separation of airflow. And if this airflow separation is near ailerons, we lose lateral controllability.
And the solution is making the flow turbulent.
By adding slots in a wing at correct positions, we are capable of re-energising the flow. It is the same thing a vortex generator does (I presume).
But what device is best suited for the current case?
From an unknown source, I found:
At high angles of attack, the airflow over the ailerons can be separated from the surface. Vortex generators, positioned just forward of the ailerons, are designed to re-energise the boundary layer and help to prevent this separation. This makes the ailerons more effective at high angles of attack
(I do not how effective this reason is.)
And therefore, please consider the case of Leading Edge Slats (which creates a slot) too. At a high angle of attack, a LE slat helps by re-energising too. And If we have a turbulent flow (by employing LE slats) in the early stage, (I think) it is better than the case where we put vortex generators near ailerons, which may encounter an already separated flow.
Edit: The aspect of lateral controllability dictates the conditions where one wing can be at higher AOA than the other. Will Slats not fail to provide the desired effect due to its symmetrical effect (increasing CLmax simultaneously for both and stalling one of the wings and making into a spin)?
Does the "symmetrical effect" apply to VG and slots near the aileron too?