It requires a runtime even after compiling: https://github.com/google/traceur-compiler/wiki/CompillingOf...

> The code generated by Traceur depends on a small runtime library containing Javascript code for things like creating classes, handling spread arguments, etc. To use code compiled from Traceur, you'll need to include that too.

That doesn't sound so bad if it works well, though, right? Kind of like including jQuery so you get cross-browser code.