No expert by any means here, but i would be a bit hesitent to feed something with those whole spiral shells in it. You can order a bag of Oyster shell grit from one of the poultry sites if you can't find it. The Oyster grit I feed says Oyster shell on the bag, and looks like crushed up white...
I have fed every single egg shell from the girls right back to them after I eat their eggs. I just wait until they are dried out, crush them out, and drop them in the feeder with the oyster shell. They go nuts as if I just gave them a treat. They must taste good!
Thank you for the article...