use monotonic consistency

- using monotonic consistency allows us to connect to secondaries.
  Since we only do reads, this has no downsides over the 'strong'
  consistency level
You are correct.  You could specify the Primary as your host with monotonic mode and it will attempt to read from secondaries, so the comment is not entirely true as written (I meant that it does not have an effect on actual consistency, it does have an effect on how it works).

The main reason for the change is because with the default 'strong' consistency, even if you never do any writes and use connect=direct, reading from a secondary will fail.