I don't know the exact details, but for whatever reason they say that heavy loads and big craft need wk....... it's on the naza webpage second paragraph down.
There is not "heavy load limit" for the naza. In my opinion a quad with 12x3,7 and 5kg is far beyond the limit, should be an okto, or more with that propeller.
This copter has about 4kg:
This hexa also about 4kg (now I have the WKM on this hexa, and there is no noticable difference):
FerdinanK, let me make 2 more questions: what is Z15? is there any difference about the ability to deal with strong and variable wind between wkm and naza?
ps.: everybody talks about my configuration, but it surprinsingly flies very well. I can get 15 min with all video equipments.