I only have 4-stroke experience with my O.S. 91 Surpass (not the Surpass II) and I must say I love this engine. I have it mounted on an Ultra Stick 60. Generally, I break in my engines in the plane. This one started for the first time on the secord flip by hand. I barely had to adjust the needle valve, it was so close. Set the plane on the runway and handed the sticks to my instructor for the planes maiden flight. He took off, trimmed it, performed gentle aerobatics, then landed without a hiccup from the O.S. This engine has performed flawlessly since day one. I'm sure the Saitos are terrific engines but because the O.S. has performed like it has I probably will stick with that brand. Good luck!