In terms of effective feedback, offering advice ONE trait at a time is the way to go.
Feedback that is highly focused on a single trait is most effective.
Think of the 'praise sandwich' approach: specific traits based praise for a writing strength is the bread. A focus on ONE area for improvement with a writer's trick is the meat and garnish.
Also don't feel you have to assess for all the traits every time. Scoring many papers is the best way to learn the traits. Scoring one trait at a time is a way to lock in the concept.
Quick feedback on the accuracy is essential as well. That's why the NWREL database of sample papers is such a treasure: http://apps.educationnorthwest.org/traits/scoring_practice.php
In the real world where you have hundreds of papers to consider, assessing all of the traits isn't effective.
When I was teaching I had between 160 -180 7/8th graders. At first I tried to do three full 6-traits assessments a year. Then it was two, at the end, just one.
Why? Because I'd burn out on the assessment and the kids got very little from my efforts. Once something is 'assessed' at that level, it's done and young writers usually won't pay much attention to advice on a finished project.
I decided to put my time into direct coaching and started doing much smaller paragraph level assessments when I absolutely had to have a 'record' for the grade book. I used a modified portfolio system, but it wasn't a commonly accepted method in the very small rural district where I worked for most of my classroom career.
The larger global assessment was usually reserved for the 'publication' pieces. I think back on the huge work of preparing publications and look up on the book shelf at a dozen books created by my classes and just shake my head. It's fine to have something tangible.
Now I wish all of the work was online. The KMSoul project was done about 10 years ago, the last year I was in the classroom. That was back before it was so easy to publish online ( a far more effective way to motivate kids than a bound and printed book because on the net they have a much larger peer audience).
I hope this little personal narrative helps!