To extend this: Cambridge Rolls: Doesn't need even soil. Won't slide to-and-fro. Doesn't need additional weight. Doesn't need filled and drained of water ballast. Can do very shallow tillage/breaking crust. Can be run over broadcast seed to work it down in, works better in chains of 2. Pushes smaller rocks down but rides over the large ones. Reduces sheet-off of light rains. Crushes mulched/left straw, hay and shreddings to the soil. Only crushes the stems in about 1/2 an inch at every 3 inches. Rattles very nicely. Hides from you at noon in even the most whispy grass. Flat/Drum Roll: Mixes the water you put in it with rust. Makes a flat pretty surface in already perfectly tilled soil. Jerks at your tractor. Crushes the stems and top roots of the whole width of plants with enough weight. Will slide downhill and take your tractor with it sometimes. Explodes in the winter if you don't drain the water. Requires bearing grease regularly. Visible from a distance in sunlight.