"Diamonds are a girl's best friend." This asset won't work out of the box, because it needs two materials and different shading. It's high poly, because the subdivision modifier had to be applied to the ring. The diamond mustn't be subdivided. The material settings and the diffuse texture are quite useless. They only exist, because MH needs them. I'll provide a tutorial on how to make this asset look right in Cycles.
CC0 - Creative Commons Zero