Yonex nylon/plastic shuttles are precision products made in Japan. They have similar flight characteristics as a natural feather ball. They are available in different qualities and speeds. For halls with poor visibility and/or light background we recommend yellow shuttles. Normally in Switzerland, the average speed (blue) is used. Other speeds are only permitted or recommended in high altitudes (eg in the Engadine or in the Jura) or in extreme weather conditions (temperature, humidity). In badminton, the used speed of the shuttle is thus defined by the rules or by the referee (if available). It is only changed by the mentioned external geographical or metrological circumstances. The game level or wishes of the players do not matter. At least not technically.
Of course, at lower levels, it is often played with slow shuttles, because it makes the shuttle easier to control. Or with fast shuttles because those can be hit from baseline to baseline. The number next to the name "Mavis" makes a statement about the quality of the shuttles. The higher the number, the better the product. There are very different qualities in plastic shuttles: