Not sure why i didn't see this post before, a subject that I've had much lively debate about on other forums! The claims made for KF airfpoild are to be blunt nonsense. I actually shared a few emails with the inventor Dick Kline a few years ago, he's a really nice guy but knows 'zip all' about aerodynamics. There has been quite a bit of testing in wind tunnels of the KF airfoils and without exception the results are terrible!
Having said that, for a powered trainer it's not a bad choice, mainly because it's easy to build and strong. The efficiency is very poor but that's not important for a powered trainer.
I actually did some testing years ago with my Elf discus launch glider to highlight the differences in lift/drag performance. I build a KFm wing that was exact same shape as the stock Elf glider wing and weighed the same. Flight time was a little over half (actually 60%) of the standard wing. The best i got with the KFm wing was 46 seconds which actually isn't too bad and at the time I think was a record for a KFm discus glider... but it was still miles short of what the standard wing can do.
I dredged these photos up:
Standard Elf:
KFm Elf: