Agreed.
Anything that gets the attention of other drivers without bothering or distracting them should always be encouraged.
But I think there is no universally 'safest place to ride', because everyone rides their bike differently.
Overall, I find that driving on the highway requires more focus, because you have very little reaction time. In addition to that, in my opinion, the majority of aggressive and impatient drivers are found on the highway, because they expect to be able to go as fast as they want. If traffic is slow, then you can bet there will be people who think they are better than everyone else and are entitled to cut other people off to get where they're going.
I also think normal roads are more safe because the hazards are predictable. You know to watch out for intersections. You know to watch out for people making left turns. But on the highway, the danger is never as obvious, because you don't know when or where someone is going to cut you off or forget to do a shoulder check.