Good question, mine are on still but Ive seen alot of guys with the honda/hs in frame who ride with them off. The fins on the fly wheel do help to cool it with the shroud directing the air flow to the block.
I currently have this engine on my BMP friction drive set up. I also have a Honda GX35. There's not comparison between the 2 engines. The China 2 stroke will out perform the Honda, hands down. A half horse power makes a big difference in these small engines. I'm sure the Honda is a good engine and will probably out last the China engine, which has more power, torque and higher top speed. I know nothing about the Honda 50cc.
