I didn't notice any significant differences in formula and application between the two polishes. I used 2 coats of each polish, but the Essie could possibly be a one coat polish if you're careful with your application. Evvie is on my thumb, middle finger, and pinkie while School of Hard Rocks is on my ring and index fingers.
Indoor Natural Light
Indoor with Flash
School of Hard Rocks is lighter than Evvie. So not dupes, but cousins. They have the same dusty green base, just a few shades apart. If you like this color family, the two polishes are definitely different enough to justify owning both.
Disclaimer: Some of the product(s) in this post were sent to me by the company for consideration.