The issue with egg shells is that feeding them can encourage some birds to become egg eaters. Once you get an egg eater in your flock, it tends to spread.
By the way, for fertilizer, bone meal in addition to the calcium is used as the primary phosphorus source. Phosphorous is required in a chicken's diet in order for them to be able to absorb and use dietary calcium. If you have an extra spot in your mineral feeder, some suggest providing free choice phosphorous to your laying hens so that the calcium you are providing is sure to do its part.
So, I would say, yes bone meal is a good thing to include. I'd leave it out free choice rather than mixing it into their feed, though.
By the way, for fertilizer, bone meal in addition to the calcium is used as the primary phosphorus source. Phosphorous is required in a chicken's diet in order for them to be able to absorb and use dietary calcium. If you have an extra spot in your mineral feeder, some suggest providing free choice phosphorous to your laying hens so that the calcium you are providing is sure to do its part.
So, I would say, yes bone meal is a good thing to include. I'd leave it out free choice rather than mixing it into their feed, though.