The Oren-Nayar node is a core Bella diffuse substrate, and we choose to call it that, because that is the model it uses, so people can learn about it from well-known sources.
As for how common it is, you will find it used in Arnold, Cinema, Corona, Inidigo, Cycles, Thea, Octane, and many other applications. In some cases they will have a distinct type named for it, like Bella, while in others it will be one of multiple shading models available for a general diffuse shader/material. In others, they may use it — or some other model — without saying so, leaving people to guess.
When you use a Bella Metal, Glass, PBR, Uber, or Principled material, you may be using Oren-Nayar without seeing the name. In some cases it does not appear at all, while in others it does, through a Roughness parameter in a diffuse component of the material.
The trick, for us, is to satisfy both people like yourself, who don’t want to know any of this, as well as others who definitely do want to know exactly how they are constructing their materials.