Hi,
If memory serves me correct (and often it doesn't). From the 208 course in Whitcita.
It was an after thought to aid in the prevention of flow seperation over the flap section, you will also see rubber VG's on the leading edge of the flap outboard section as well. Hope I'm right there, little while since I've been near the van.
Not quite sure how it effects boundary layer control to mitigate flow seperation, perhaps it is a similar principal to that of the trailing edge "cup" on high performance boat props. Maybe.
Love to hear from others how the trailing edge strip helps boundary layer control on a flap, if in fact it does. I believe trailing edge strips on control surface are to reduce control forces, blunt control trailing edges achieve the same to I believe.
Regards
M