Been investigating Mantra a bit more now. It's a very capable renderer. At first it was a bit daunting, but the flexibility of creating your own shaders using VOP's is amazing.
Here are two renders of car parts. Kit bashed from various models I've collected over the years. I did some UV'ing and modelling tweaks in Houdini. All the shaders are Principle core, and then expanded with some of my own creations.
Using my rounded edges shader as a base, I made a one that adds edge dents. Helps give the objects a worn look. You just calculate the edges once, then use that as a mask to drive the color, spec etc. It uses raycast below and above the surface an returns changes in angle it finds.