Yes, he is serious. It depends on the property type. I mostly use 21's and they work great. But all my lawns are smaller and "postage stamp" where as yours may not be. Would I mow 3/4 acre with 21's? Heck no. I doubt justmowit is sitting back laughing. Although I thought his story and his plan were great, I just don't see it working. I hope he can comment on this. Hard to believe no one talks to him?