The Bookshelf scene is very difficult to render with unidirectional path tracing due to complex glossy interreflections and light sources encased by glass. Radiance-based path guiding is highly effective at rendering this scene with the GMMs by Vorba et al.  performing the best among all radiance-based approaches, closely followed by our NPG-Radiance. Our product-based path-guiding approach is able to improve upon the radiance-based GMMs, but only by a tiny margin. Primary-sample-space path-sampling techniques offer little to no benefit over unidirectional path tracing with our NPS slightly outperforming PSSPG [Guo et al. 2018].