Can't help with advice on the World Models Extra .30 but I can tell you that I love my Modeltech Extra 300 .25 size arf. I am running an O.S. 32 sf on it and it will do everything you will ever want to do. Knife edge is neutral and it will flat spin with left up snap switching to down elevator and then slowly crossing the aileron. I mean flat! Then the light wing load allows it to slow way down for very nice landings. All that for under $100.00 for the kit. It is the first plane I have liked enough to buy again if I stuff it in. Hope this helps confuse the original question.