OK this is just my opinion and one should always make their own choices, so take it with a grain of salt please and don't freak out about your own flock choices just because something didn't work for someone else OK?
I did not like it for my flock. I started with a dozen day old chicks and had them on medicated Purina Start & Grow feed. They all grew well and thrived. Right at 8 weeks (which is what Scratch & Peck recommends) I switched them to S&P grower. They had already been provided grit and were fully free-ranging our half acre. For 5 weeks after that (until just last week!) I agonized over whether or not my girls were eating enough, drinking enough, and growing enough. My conclusion was that they were not, and it was possibly because the whole grains weren't being easily digested by the little pullets at 8-12 weeks old. Also possible that because I took them off medicated starter and they were already outside eating GOBS of earthworms daily, maybe they have had a small load of Cocci in their guts which was hampering their growth. Also, many of my birds who I had sold (order split) to a friend who had stayed on Medicated starter through now and were the exact same age and breed as mine (same hatchery, likely siblings), her birds were MUCH bigger with bright red combs and wattles (no they weren't roosters) and mine remained growing slowly with very pale yellow combs and wattles. I also noticed that most of our birds didn't like to eat the "crumbs" of the feed (which is where the nutritional content lies with all the vitamins and boosts they put in) but only the whole grains, and I'm not the kind of chicken mama who will scoop out all the extra crumbs daily and make it into something else that the birds will eat. I love my birds but I also need easy and fast chicken care since I'm a home schooling mama of 3 small children with a too-big house to care for and LOTS of laundry to keep up with! So, long story short, we recently switched back to medicated starter/grower (Purina) for the whole flock of now 11-14 week olds and they are once again thriving and seem to have had a growth spurt in just the last few days since the switch.
PLEASE take what I said with a grain of salt. We all have different chickens, different climates, different soils, different coop/run setups, different free-range plants for our chickens to access, etc. The minute differences in all of our flocks are endless. But I would ask that you keep an eye on your chickens for the first few weeks and consider if they are still staying healthy and growing strong. I'm like you and LOVE organic, non-GMO, soy free, corn free, etc. I cloth diaper, don't buy or use any paper products EVER, only chemical free household products and cleansers/ personal care items, yada yada. We're all natural here and try our best to do everything organically, but in this case it wasn't working for us and I'm OK with our recent decision. I am, however, hoping I can switch everyone to an organic layer feed down the road, but we'll evaluate that when the time comes.