I pre thin the paints I'll be using and obviously the primer as well so it's ready to go when I need it so in that regard it doesn't have to be different than pre thinned primers. Sure it's slightly more convenient to have the paint pre thinned but It's not that hard to do and you can do it in a large batch and not over and over every time you need it , so I see that advantage as marginal. Also Mr color paints and their primer are extremely easy to thin.