Using Critical JS with Now Zeit

I'm trying to use Critical for deploying a static website on Now Zeit.

For using critical on a remote server (like Zeit Now) it seems I have to use puppeteers and Chrome.

Zeit seems to permit it, and the documentation gives some info about it here:
https://zeit.co/blog/serverless-chrome

I'm trying to follow the documentation but I'm not so into puppeteers so it looks I miss some steps.

Anyone has faced the same issue? Maybe give some tips or some repo examples?

Maybe off-topic, but I would like to ask anyway