It doesn't make them want to eat eggs, I've cracked some eggs open for mine on the spot and let them eat them. Of course, my way makes them want to eat broken eggs, but I have no use for broken eggs anyway
The reason I said to put them in a separate dish is so they don't make the feed spoil...
You can feed them any kind of shell, though I'd put it in a separate dish and not in the feed. I think if you plan to give it to them as a supplement you should bake them for a while. I just mash my eggs up shell and all so I don't worry about that. As for opening them easier, try this...