G'day, Andy. Thanks for asking. Maybe the best info on the STOL kit is from the guys who make it. Go to
http://www.steneaviation.com. Read the STOL kit description and information.
When I was researching, I looked at (1) a kit that integrated flaps and ailerons, (2) vottex geberators, and (3) the Sportsman cuff from Stene.
Option (1) is complicated with moving parts. As the flaps are lowered, the ailerons also droop. My first concern there would be reduced lateral control. My second thought was rigging all those bellcranks in there. My third thought was asymetrical roll if just one part of the system works, and another part doesn't. I preferred fewer moving parts, not more.
Option (2) Vortex generators (VGs) add no moving parts, and are quite effective, especially when coupled with the Steen Sportsman cuff. But that gets to be a lot more money. And, the VGs have to be treated very carefully or they get knocked off of the wing, vertical stab, or horizontal stab. If two or more are missing the plane is grounded. Not a robust solution.
Option (3), the Stene Aviation cuff was simple, has large effect (nearly doubles the lift component), and adds no moving parts. Revisit
http://www.steneaviation.com. It changed the character of the plane. Now, slow flight can be done with a clean wing - no flaps. A power on stall doesn't stall, it hangs on the prop. Final is straight and stable. With the original wing, especially Cessna's old wing like the Duck has, final was jigging and jagging with me hanging on and trying to keep up with what was going on.
It also dampened out the SLAM that had been being delivered by thermals. Now, the plane rises and drops as we fy along - but gently. No longer is it like blindly hitting a large pothole while driving along, and getting slammed all over.