Not only is there no advantage to using NLP over Photoshop/Lightroom, there are some big disadvantages. If a negative is inverted using NLP in Lightroom, then forever afterwards many of Lightroom's adjustment tools work backwards or in unexpected and useles ways - that is, unless you take further steps to export the file as a TIFF and then re-import it into Lightroom. NLP essentially cripples many of the sophisticated tools you paid for in Lightroom. I might tolerate NLP invalidating Lightroom's normal tools to get accurate colors - but for b&w - no way.
For b&w, I prefer to open the RAW camera-scans in Photoshop (via ACR), and invert to positive in Photoshop. For one thing, Photoshop has superior tools (compared to Lightroom) for removing dust and scratches. And in Photoshop, I can apply corrections to local areas of my images - which I can not do in NLP. After I get the b&w positive looking pretty good, then I will save that as a 16-bit TIFF in Grayscale, and import the TIFF into Lightroom - where I can add Captions, Keywords, etc. I also wait to do any cropping or toning in Lightroom so those changes are non-destructive and reversable.
BTW, if you are digitizing color slides, I don't believe NLP is any help there, either.