In my view i called $model->related1, and it worked, so i suppose the framework find itself the relation and did the good query. But the query was duplicated.
The ORM supports what we call "lazy loading", if you request a relation that wasn't loaded in the original query, the ORM fires a second query to load the relation. If you know you need the relational data, it is usually better to include it and use a join.
Whether or not that is better or faster depends for a large part on your choice for RDBMS, the installation and tuning of it, the hardware it runs on, and your database design.
In theory a join is faster than seperate queries, but it could well be that due to your local circumstances, that isn't the case for you.
If you use MySQL, the profiler also includes data from the query analyzer, which tells you how the query is run (in terms of indexes used, area sweeps, on-disk-sorting, etc), which in turn can tell you why a query is slower than expected.