I'm looking for some insight from someone who owned both Redux and the standard beige version. Looking at their website, the Redux lineup seems to be worse by a slight margin than their brown counterpart. Looking at some online reviews, the results are opposite. The most comprehensive tests I've found are from CoolingTechnique and from their results, Redux are noticeable better. Searching for other reviews and forums, the results are mixed, some say they are noisier, other say they are better but no one seems to have own both of have a clear answer.
A while ago I bought a pair of P14r Redux PWM for my NH-C14: with reference to the original brown/pink P14, I didn't found any really noticeable noise difference at my usual speeds (around 200rpm at idle, around 600rpm at load: being differently controlled their settings are different, 10-29% duty cycle vs 25-50% voltage, and the Redux are more effective at full speed because they actually spin faster, 1500rpm vs 1200rpm).
Broadly speaking I'm fully satisfied by both these fans.