The Rhino plugin makes things really seamless. I use that 99% of the time. The last 1% is that I prefer to keep working on Rhino while rendering in the background so I call the BellaExport command and it auto-opens the GUI. to starts rendering as a separate process.
There is one issue with Rhino viewports that once you assign Bella materials then the other modes (eg render mode) gets wonky, or black, because assigning emitter to surfaces confuses Rhino into thinking there are no lights in the scene. This is as much a McNeel issue though (was discussed before). Also although you can use the native Rhino lights, you loose the ability to use lumens or Watts on those, because Rhino (McNeel side) doesn’t have that interface implemented.
Bella is heavily nodes based and currently neither the GUI nor Rhino have a nodes graphical interface, but I think there is some consideration leveraging grasshoper’s UI. If you’ve seen Blender’s material node system, Bella will be like that graphically at some point (is my understanding)
Bella has two engines (a fast and a slow). The fast engine works for most scenes and it can also show dispersion on gems, but does not throw caustics. On speed it has an edge (or on par) with CyclesX already, but they haven’t finished the GPU support yet.
Currently displacement is not yet implemented, but bump and normal maps work well.
You can create material blends which works like Maxwell’s layer system, but more versatile.