It's night and day from what I used to fly, I really love it!
What did you use to fly?
I haven't noticed a huge difference between unmodified Cessnas and those with the simple STOL kits like yours. They do fly a little bit slower and have a more docile stall, but just no "smoking gun" change in performance. With my unmodified '57 182 I was able to takeoff and land in under 300' at moderate weights (2 people plus gear). (The takeoffs and landings were done at a Short Field clinic put on by the Alaska 99s -- they were doing the measuring).
A mod I did see a huge difference in performance with was on the Turbocharged P206 I was hauling jumpers in. The first year it was a stock airplane. My takeoff technique is to just use a little backpressure and let the airplane fly off when it's ready. With the unmodified 206 I'd liftoff around 60-65 mph. Over the winter the boss installed a STOL kit consisting of the cuffed leading edge. He also installed the WingX Stol wing tip extensions (IIRC it was 18 inches added to each wing) AND he put on a Vortex Generator kit. It was a whole new airplane. Using the same technique the airplane would not come off the ground around 50mph. With just me or one other person in the airplane it wouldn't stall power off. With the yoke all the way back to the stop it would mush wings level. Time to climb to 12,500' was slightly improved. I could fly a steep approach at 50 IAS and felt safe doing so, still had energy to flare. I think the biggest performance gain was due to the added wing area. The VGs helped make the elevator more responsive allowing you to have positive pitch control at very low speed.
He did these mods to both of his 206s. One fall we used them to take his family and friends hunting, landing near a glacier on a little strip about 600-700' long. It was a no sweat operation in and out. We weren't loaded to gross, but we certainly had a good payload on the airplanes.
If I were to do a mod for short field work my first choice would be the WingX STOL extensions.
