Leovince exhaust are exhaust for standard 50cc cilinders, they hardly go faster than the standard exhaust! Other exhausts like yasuni R, giannelli shot, polini for race are way better and match "low" reving 70cc cilinders.
Yasuni City 16 is the "legal" verion of the C16. Don't know much about it. If it is about the same as the real C16, it can go on 50cc but it isn't the best choice. It's an exhaust for midrace setups like stage6 racing, airsal70 etc.
The city16 is legal becaus it is restricted. With this restriction is runs even worse than a leo