Susun weed (of 'Wise Woman' tradition) advocates adding this kind of calcium to her herbal vinegars, If I'm not mistaken.
You can google her... sounds elegant and simple, yes?
I've wondered about this too...I make herbal vinegars, sometimes doubling or tripling them, (as I've read a forum member here does, with lemon balm.)
Something in me resists -making- this eggshell calcium--(and I give it to the plants/compost)I wonder sometimes if it is only that I don't know exactly where the eggs come from-->>I doubt the 'happiness' of the chickens.
In fact, I've only recently started to eat eggs--after a long time of being vegan, mainly.
(pS I just read uniquity's answer...and I'm glad she's glad...)