There are million brands of shuttlecock out in the market. How can you decide whether it's good quality shuttlecock?
Normally, BWF approved shuttlecocks are belongs to top quality shuttlecocks because they will be use for national or international shuttlecocks. However, BWF approved shuttlecocks usually sells quite expensive and it's not 100% assure that is top quality.
The best way to find out is trial and error. Different temperature and humidity can affect shuttle speed, places like Malaysia use speed 75-76, NZ winter use 78.