I’ve been having a serious look at using spheres and also boxes to represent the collision
shape in bullet simulations. Spheres are great in that you can rely on the geometry to not get caught and hang on to each other. Boxes offer a nicer settling motion in certain setups too. The main reason I wanted to look at it, was to avoid always needing to use glue constraints. Sometimes I want a nice quick voronoi fracture that uses the clustering option, and this yields shitty collision approximations with convex hulls.
Enter vdb sphere packing! It allows me to fill the wacky geometry shapes and use those as colliders. I just save out my points, and transform the original pieces. Voila!