I agree. At that age, they need the proper protein, vitamin and mineral levels in their starter and scratch will mess that up. Best to wait on it for a few more weeks at least, and then, only use it as a training tool, like shaking the scratch can to get them to come when called then letting them get a tiny taste.
I always use chick scratch with my birds in the brooder. I feed small grit in their mash so they can properly digest it. I spread the scratch over their bedding to encourage them to keep it turned up and fluffy. Their regular ration is fed free-choice and the scratch I only put down twice a day in limited amouts. .....Alan.