NP3 hasn't existed at a consumer level for over a year. Black Nitride and NP3 are completely different, chemically speaking. NP3 is a nickel plating infused with Teflon. QPQ Black Nitride is closer related to case hardening, but iron nitride/oxide and salt baths. Also known as Melonite or Tenifer.
A Gen4 or Gen5 Glock pistol is a prime example of QPQ Black Nitride...but Glock calls it Tenifer.
NP3 adds considerably more dimension to a part, when compared to a nitride finish. Something to keep in mind if you are refinishing internal components.