Just a quick note to say that I have a project which needed a lot of conveyor belts, to move objects along, and implemented it with `rollers`, like 5 rollers per block. The rollers had to rotate with a script, and have a physics material with some friction. Performance was not super great. When I switched out these for surface effectors (unity 5), applied to a single rectangular 2d collider, physics performance more than doubled! So now my scene which was `too slow` even for my iPad Air, is now running nice and smooth. Thanks Unity!