I run it in a production environment (side project). I also use it locally when developing when necessary.

It really does speed up loops by 5x or so.

So when you're trying to say... test 100 million+ iterations of something, pypy will run that in something like 2 minutes versus cpython can take me 15 minutes.

Honestly it's an amazing performance gain for 0 effort, and I have yet to run into a limitation with it.