This is my comparison of Revlon Perplex (Chanel Paradoxal Dupe) and Sephora X - Secretive. I didn't even think of comparing the two until someone made a comment when I posted my review of Sephora Secretive that it looked like Revlon Perplex.
As you can see - the base color is pretty close. The difference between the two is that Secretive is a creme finish and Perplex has the subtle purple/pink shimmer. To tell you the truth, I wore the alternating look above all day and unless I got really close and studied the differences, I couldn't really tell. I have never thought the shimmer was very evident in Perplex on the nail. I took quite a few shots and this shot showed the difference between the two the best. For the most part - depending on how the light hit the nails, I couldn't see the difference in my photos.
They do look a little more different in the bottle, but I think Perplex looks a little better in the bottle than on the nail. That's just my opinion. In conclusion, they aren't exact dupes, but if you already have Perplex, I would suggest checking out some of the other Sephora X polishes as they have so many unique shades. See my prior post that links the collections here.
I hope everyone is doing well!