I first tried Black With Envy on its own. It was a two coater for me, and I had no issues with the application. I did have some issues with clean up, but that was operator error. (If you click on the third photo below you can get a good look at the divot I made in the polish with my clean up brush.)
I then got out my Chanel Black Pearl and did a side by side comparison. On the nail, I found the Revlon a touch darker, and its shimmer was less frosty.
Are they dupes? No, but they're close, and the Revlon is an attractive alternative, especially for the price (I think I paid not quite US$5).