Works great for me. There's some minimal configuration explained in the pgbouncer docs. What the pgbouncer buildpack does is just route your DATABASE_URL through the local pgbouncer.
In my python app, I switched from an sqlalchemy connection pool per process (eg per gunicorn worker) to using a Null pool everwhere. No increase in latency; far fewer connections needed.
Or would you have to roll your own pgbouncer setup for these systems?