I started using NIK when Color Efex Pro 3 could be purchased and integrated with Nikon Capture. Fast forward to today, I use DXO PL5.5 Elite edition and NIK Collection, primarily CEP and Silver Efex Pro. In CEP I love using Pro Contrast and Tonal Contrast to make subtle but important adjustments using the highlights, shadows and mid tone sliders. For most of my nature images I also use Darken Lighten center to emphasize the main subject.
If you are a Photoshop user (I am not) NIK can be used as a layer and Smart Object. Google this to see how it works. This can really benefit your processing in PS.
Get the most from using the Nik Collection in Photoshop. This tutorial and video explain techniques to make using the Nik Collection in Photoshop easier.
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When you select Deep Prime noise reduction in DXO PL5 Export to file does take some time. If Deep prime is not needed, Export to file is pretty quick.