Immediately after seeing this I felt the need to mock it.
Sure, plants growing out of egg shells are cute, but the text touts this as a way to recycle your cracked egg shells. Of all the things we need to worry about finding a way to recycle - egg shells aren't one of them.
They recycle themselves, pretty easily in your compost, have been for years.
If you'd rather plant seeds in them by all means go ahead, but don't pat yourself on the back over all the egg shells you're keeping out of the landfill.
Then I thought - "you're such a curmudgeon Joanne, just let them have their cute seedings in egg shells - what's the harm?"
I suppose the harm is when we think that we can rest on our green laurels after recycling egg shells and therefore don't address any real issues.