The bottles:
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Pretty similar here. The Chanel looks a little more sparkly, but that could just be the bottle shape.
The brushes:
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Surprisingly similar. The Chanel version has a slightly longer handle and the bristles are a little shorter, but that's about it.
And finally, the swatches:
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I have Chanel Paradoxal on my pinky and middle fingers, with Revlon Naughty on my ring and index fingers. Quite honestly, I can't tell which is which! They are practically identical, from the subtle pink shimmer to the gorgeous greyish purple. The Revlon version might be a touch darker in this close up shot, but I could not see a difference in person.
Application for both was very similar - no real issues at all with either formula.
In this case, we definitely have a true dupe. Unless you're really concerned with the label on your polish bottle, you can safely skip the $25+ on the Chanel, and pick up the Revlon. I've seen it on sale for as little as $3 a bottle.