The author does not seem like an experienced Node.js developer. All those

    if (err) {
      done(err);
    }
    else {
      // ...
    }

are usually written in this style:

   if (err) return done(err);
   // ...

I personally don't like promises and tend to avoid libraries who use them. I don't really see the problem they are trying to solve which is not already solvable in a more flexible way through libraries like async.