I used non medicated organic on our first batch of pullets ( almost 3 months old now). We bought a 50lb bag at the feed store and they said it would be good to feed them all the way until they were ready to lay. We raised them in a brooder with a hardware cloth floor and took great pains to manage their environment so they wouldn't get sick, but they ended up getting Cocci after a day trip out the the garden (we live in a damp climate with lots of wild birds around).
We went out and got Corrid (amprolium- same stuff in medicated crumbles- just more concentrated) and some antibiotic feed additive for them and they recovered pretty fast. Thank goodness!
By the time they were about 9 wks, we were just finishing up the end of the bag of feed when our speckled sussex (who had the worst of the cocci) got really sick and we had to cull her. We aren't sure what she had yet, but her symptoms were consistent with eating something moldy... the people we consulted when she got sick asked what type of feed and told us that the organic feeds don't last as long as the non-organic and our feed may have gone bad. Her immune system may not have recovered from her bout with the cocci and so... anyway, it was sad but it happens.
For our second batch of pullets (1.5 weeks) we decided just to use the medicated crumbles for them- we want them to build up their immunity to the cocci gradually. We will switch them over to organic feeds about a month or so before they start laying. Ive heard that is how long it takes the amprolium to work through their system.
Its all trial and error, i know lots of people who have used the organic non medicated and never had an issue
Really my only advice is - if you go organic non medicated- buy a small bag of it because it doesn't keep as long, Keep your habitat dry and clean, bring little bits of earth in for them to get exposure to gradually, and keep Corrid on hand just in case. But if you already have the medicated crumbles...why not just finish them out? if you are raising these for eggs and want organic- switch over to the organic feed no less than 30 days before they start laying.
Good luck!
sorry it got so long-lots of coffee!