The "dramatic" improvement is subjective I will admit. I ran the same experiment with a 33% laser and a Kaos. The difference was mainly at the ends of the envelope. Slow flight got better and fast forward flight felt more locked in. The 33% laser with the Flat tail just was a flat pig in a TR. If you strayed a few degrees out of verticle it was flopping over like a fish. The design with AF tail had almost to much bite you could kick it from 45 deg off heading in a hover and all the way to 45 deg the other way at will. The slow flight was incredible- solid as a rock. I felt it gave a large improvement to the overall performance. The Kaos felt less jumpy and locked in as well. It had a little more power in control response like in slow rolls and snaps. It helps to give more power but also more even response from the surfaceor more lienear (sp) input.

I think it has to do with the airframe and what kind of flying you do as to its worth. An Ugly Stick would not be helped much but say a more precise aerobatic design would be helped quite a percentage. It gives that little bit of an edge in control IMHO

Regards
Bill