ES6 execution could be slow?

http://www.incaseofstairs.com/2015/06/es6-feature-performance/?utm_source=javascriptweekly&utm_medium=email

Conclusion from the article :

Personally I intend to start using most of these features where they
make sense but will avoid designing core APIs around these features
(perhaps with the exception of Promises) until the native
implementations have matured a bit.