I've always fed medicated chick starter, and have never had any problems with coccidiosis. I've always bought Purina Sun Fresh at my local feed store. Recently when they were out of it, I went to the "other" feed store in town. I don't shop there because they don't carry Purina, but rather Cleveland feeds which have a lower protein content.
Anyway, when I asked for medicated chick feed, the man said (in a gloom and doom voice) "NO ONE feeds that! It's full of STEROIDS!"
I wanted to say, "Um, I think you're WRONG. It has amprolium in it to HELP prevent coccidiosis."
But I didn't. He owns a feed store and obviously thinks he knows everything about feed. I told him I would keep looking. I called all the feed stores in a 40 mile radius and found one that had medicated chick starter. Unfortunately it was made by Cleveland, but I drove out there and bought it anyway because I was just plain OUT of chick feed. It has been fine, and the chicks are still healthy and happy.