Tempering the chocolate isn't necessary, but it will prevent your chocolate egg from 'blooming', that is, turning a matte, greyish colour after a few days. Tempering ensures your chocolate egg will be shiny and look that little bit more professional!
I made this before and the eggs didn't come out of the mould. They tasted good though. - 16 Nov 2015 (Review from Allrecipes UK & Ireland)