YS are awsome engines when they are running right. They tend to have a LOT more fuel system problems. Sooner or later you will get to experience the joys of a tank rupture
(hopefully not inside an expensive airplane). You tend to become very familliar with the disassembly and cleaning of the regulator/carburetor. Many pattern flyers end up with two because one of them seems to live at YS Performance. Standard fourstrokes may be less powerful but they are easier to live with.