I've been trying to make a couple of ivory tipped strikers everytime that I turn something. They are kind of a pain in the butt to make and ivory is not the cheapest material to use.
With that said, I have ran every one of them on calls that I have here ready to go out. Sometimes there is little difference between it and a wood striker. I had a guy interested in one to go with his call the other day and told him that I had ran one on his crystal call and didn't notice enough difference for me to justify recommending one to him.
On other calls, I have noticed some more rasp and a little more sound out of the ivory and would recommend it over wood. I have a ceramic call here and a cocobolo/ivory striker that I made for myself that sounds better than any other call I have ran one one.