The only or rather main difference will be protein level and whether they are medicated or not. Most other differences are minor.
I feed everyone Purina flock raiser with 20% protein and about 1% calcium. It works well for my chicks and my adult birds with oyster shell on the side for active layers. My birds are always at different stages in life.
Grower, finisher, flock raiser, all flock, starter... all confusing terms and each company uses their own. The tag sewn on the bottom will tell you the guaranteed analysis for the most important nutrients. I saw starter at Wally, maybe manna pro that was ONLY 18%. While some growers are 18% and some other starters will be 20-22% protein.... The label at the bottom also has the ingredients listed. I buy what's available to me at a price I can afford and a recent mill date. This may vary by region and by store I pay as much as $3 for the same feed. But freshness matters to me. One other difference I can think of in feeds might be pellets verses crumble. Small chicks may have a hard time with pellets.
In other words.. feed it too them when you want... just not layer since the protein is low and the calcium is high (for growing non laying birds). Keeping it simple works pretty well!
If they haven't ventured outside yet, maybe bring in a plug of dirt. Grass, roots, and all. It works as great enrichment plus exposes them to some of the bacteria on your pasture before they go out full time so they can build some resistance. Presuming that it's pesticide and herbicide free.
Most importantly to me... don't feed scratch. But if you do, NOT more than 10% of their total daily ration since it is low in protein and doesn't have the added vitamins, minerals, and amino acids that a formulated ration does.
Sorry so long... but hope it helps.