That feed contains everything they need for a balanced diet. Everything. Vitamins, minerals, protein, fiber. If that is all they eat they will do fine.
The general rule of thumb is that anything else should amount to no more than 10% of their diet and they will still get a balanced diet. In practical terms, if they can't clean it up in 10 to 20 minutes then it's more than that 10%. You can feed them other things every day if you wish as long as it is below that 10% threshold.
They do not need herbs, spices, vinegar, scratch, or anything else if they have a balanced diet. Many people feed them that stuff because they think it helps but as far as I'm concerned it just makes the people feel good that they are "helping" the chickens. But as long as it is not too much it does not hurt them.
All of this goes out of the window if yours forage for much of their food. If you let them forage much you have lost the ability to micromanage what they eat. They decide that. As long as they have good varied forage chickens are pretty good about maintaining a balanced diet. They tend to eat a bit of everything.