I did look at it, but the API appears to be completely undocumented, there aren't any precompiled libraries for it (the ordinary binaries don't contain the API), and it's painfully complicated to build.
The nicest renderer I've found, API-wise, was OSPRay, which was simple and elegant to use... but doesn't support volumetric rendering in any way. I have in the past got this working, more or less, with Mitsuba with some custom code but I'd rather like to avoid customisations. They're too much work to maintain.
I personally think Mitsuba is the dark horse of free renderers. Blazing fast, good highly modular design, good docs, super easy Python bindings, GPU preview. The only problem is it's a one-man show, and the one man seems to have been doing other things lately. Nevertheless it's the renderer I think deserves to become the "standard".
