As you can see, the NYX primer makes the shadows brighter and lets the sheen they're meant to have shine through. I liken the UDPP to swatching over bare skin. Last night I did that next to it, and it looked basically the same. The colors aren't as bright, and there is no luster to them.
At $20, I feel like UDPP is just a waste of money. The NYX primer retails for only $7, so you're really getting your money's worth.
What do you think? Let me know your thoughts in the comments. Hope you enjoyed!