I have put the new Prime NR engine through a torture test with some images from a Pentax K-5II shot at ISO 12,800. There is no doubt that Prime excels at removing noise and preserving detail. In this regard, it outperforms other programs that I have tested, including Noise Ninja 4 (part of Photo Ninja) and Topaz DeNoise 5. However, Prime has a tendency to produce blotchiness in out of focus areas. In some cases, it is barely noticeable at normal viewing sizes, but in others it is a problem. In contrast, NN4 produces a fine, uniform grain pattern that is very film-like and unobtrusive.
Perhaps the biggest knock on Prime is how slow it is in operation and in rendering to output. You had better have a very fast computer or be prepared to spend a great deal of time using this NR feature. In general, DxO 9 is slow and unresponsive on older machines, and the UI is cumbersome, but it does deliver good results--better than ACR/LR but worse than Photo Ninja, IMO.